cpython-lru_cache-weakref: Doc/reference/lexical

annotate Doc/reference/lexical_analysis.rst @ 79675:c0a2294de787 2.7

Issue #16199: Backport 2to3 typo fix from 3.2.

author	Chris Jerdonek <chris.jerdonek@gmail.com>
date	Thu, 11 Oct 2012 16:15:46 -0700
parents	117d58fc6e8d
children	c0788ee86a65

rev	line source
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	1
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	2 .. _lexical:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	3
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	4 ****************
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	5 Lexical analysis
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	6 ****************
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	7
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	8 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	9 single: lexical analysis
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	10 single: parser
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	11 single: token
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	12
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	13 A Python program is read by a parser. Input to the parser is a stream of
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	14 tokens, generated by the lexical analyzer. This chapter describes how the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	15 lexical analyzer breaks a file into tokens.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	16
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	17 Python uses the 7-bit ASCII character set for program text.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	18
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	19 .. versionadded:: 2.3
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	20 An encoding declaration can be used to indicate that string literals and
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	21 comments use an encoding different from ASCII.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	22
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	23 For compatibility with older versions, Python only warns if it finds 8-bit
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	24 characters; those warnings should be corrected by either declaring an explicit
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	25 encoding, or using escape sequences if those bytes are binary data, instead of
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	26 characters.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	27
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	28 The run-time character set depends on the I/O devices connected to the program
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	29 but is generally a superset of ASCII.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	30
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	31 Future compatibility note: It may be tempting to assume that the character
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	32 set for 8-bit characters is ISO Latin-1 (an ASCII superset that covers most
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	33 western languages that use the Latin alphabet), but it is possible that in the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	34 future Unicode text editors will become common. These generally use the UTF-8
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	35 encoding, which is also an ASCII superset, but with very different use for the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	36 characters with ordinals 128-255. While there is no consensus on this subject
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	37 yet, it is unwise to assume either Latin-1 or UTF-8, even though the current
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	38 implementation appears to favor Latin-1. This applies both to the source
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	39 character set and the run-time character set.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	40
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	41
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	42 .. _line-structure:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	43
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	44 Line structure
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	45 ==============
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	46
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	47 .. index:: single: line structure
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	48
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	49 A Python program is divided into a number of logical lines.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	50
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	51
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	52 .. _logical:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	53
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	54 Logical lines
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	55 -------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	56
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	57 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	58 single: logical line
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	59 single: physical line
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	60 single: line joining
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	61 single: NEWLINE token
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	62
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	63 The end of a logical line is represented by the token NEWLINE. Statements
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	64 cannot cross logical line boundaries except where NEWLINE is allowed by the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	65 syntax (e.g., between statements in compound statements). A logical line is
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	66 constructed from one or more physical lines by following the explicit or
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	67 implicit line joining rules.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	68
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	69
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	70 .. _physical:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	71
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	72 Physical lines
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	73 --------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	74
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	75 A physical line is a sequence of characters terminated by an end-of-line
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	76 sequence. In source files, any of the standard platform line termination
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	77 sequences can be used - the Unix form using ASCII LF (linefeed), the Windows
49184 59db4b3a06b0 Remove things specific to the old Macintosh, and spell "Mac OS X" consistently. Georg Brandl <georg@python.org> parents: 48186 diff changeset	78 form using the ASCII sequence CR LF (return followed by linefeed), or the old
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	79 Macintosh form using the ASCII CR (return) character. All of these forms can be
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	80 used equally, regardless of platform.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	81
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	82 When embedding Python, source code strings should be passed to Python APIs using
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	83 the standard C conventions for newline characters (the ``\n`` character,
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	84 representing ASCII LF, is the line terminator).
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	85
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	86
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	87 .. _comments:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	88
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	89 Comments
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	90 --------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	91
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	92 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	93 single: comment
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	94 single: hash character
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	95
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	96 A comment starts with a hash character (``#``) that is not part of a string
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	97 literal, and ends at the end of the physical line. A comment signifies the end
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	98 of the logical line unless the implicit line joining rules are invoked. Comments
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	99 are ignored by the syntax; they are not tokens.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	100
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	101
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	102 .. _encodings:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	103
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	104 Encoding declarations
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	105 ---------------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	106
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	107 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	108 single: source character set
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	109 single: encodings
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	110
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	111 If a comment in the first or second line of the Python script matches the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	112 regular expression ``coding[=:]\s*([-\w.]+)``, this comment is processed as an
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	113 encoding declaration; the first group of this expression names the encoding of
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	114 the source code file. The recommended forms of this expression are ::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	115
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	116 # -- coding: <encoding-name> --
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	117
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	118 which is recognized also by GNU Emacs, and ::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	119
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	120 # vim:fileencoding=<encoding-name>
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	121
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	122 which is recognized by Bram Moolenaar's VIM. In addition, if the first bytes of
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	123 the file are the UTF-8 byte-order mark (``'\xef\xbb\xbf'``), the declared file
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	124 encoding is UTF-8 (this is supported, among others, by Microsoft's
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	125 :program:`notepad`).
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	126
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	127 If an encoding is declared, the encoding name must be recognized by Python. The
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	128 encoding is used for all lexical analysis, in particular to find the end of a
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	129 string, and to interpret the contents of Unicode literals. String literals are
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	130 converted to Unicode for syntactical analysis, then converted back to their
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	131 original encoding before interpretation starts. The encoding declaration must
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	132 appear on a line of its own.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	133
44383 3625234bf3d2 Some cleanup in the docs. Georg Brandl <georg@python.org> parents: 42603 diff changeset	134 .. XXX there should be a list of supported encodings.
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	135
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	136
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	137 .. _explicit-joining:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	138
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	139 Explicit line joining
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	140 ---------------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	141
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	142 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	143 single: physical line
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	144 single: line joining
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	145 single: line continuation
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	146 single: backslash character
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	147
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	148 Two or more physical lines may be joined into logical lines using backslash
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	149 characters (``\``), as follows: when a physical line ends in a backslash that is
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	150 not part of a string literal or comment, it is joined with the following forming
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	151 a single logical line, deleting the backslash and the following end-of-line
44383 3625234bf3d2 Some cleanup in the docs. Georg Brandl <georg@python.org> parents: 42603 diff changeset	152 character. For example::
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	153
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	154 if 1900 < year < 2100 and 1 <= month <= 12 \
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	155 and 1 <= day <= 31 and 0 <= hour < 24 \
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	156 and 0 <= minute < 60 and 0 <= second < 60: # Looks like a valid date
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	157 return 1
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	158
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	159 A line ending in a backslash cannot carry a comment. A backslash does not
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	160 continue a comment. A backslash does not continue a token except for string
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	161 literals (i.e., tokens other than string literals cannot be split across
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	162 physical lines using a backslash). A backslash is illegal elsewhere on a line
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	163 outside a string literal.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	164
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	165
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	166 .. _implicit-joining:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	167
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	168 Implicit line joining
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	169 ---------------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	170
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	171 Expressions in parentheses, square brackets or curly braces can be split over
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	172 more than one physical line without using backslashes. For example::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	173
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	174 month_names = ['Januari', 'Februari', 'Maart', # These are the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	175 'April', 'Mei', 'Juni', # Dutch names
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	176 'Juli', 'Augustus', 'September', # for the months
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	177 'Oktober', 'November', 'December'] # of the year
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	178
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	179 Implicitly continued lines can carry comments. The indentation of the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	180 continuation lines is not important. Blank continuation lines are allowed.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	181 There is no NEWLINE token between implicit continuation lines. Implicitly
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	182 continued lines can also occur within triple-quoted strings (see below); in that
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	183 case they cannot carry comments.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	184
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	185
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	186 .. _blank-lines:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	187
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	188 Blank lines
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	189 -----------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	190
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	191 .. index:: single: blank line
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	192
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	193 A logical line that contains only spaces, tabs, formfeeds and possibly a
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	194 comment, is ignored (i.e., no NEWLINE token is generated). During interactive
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	195 input of statements, handling of a blank line may differ depending on the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	196 implementation of the read-eval-print loop. In the standard implementation, an
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	197 entirely blank logical line (i.e. one containing not even whitespace or a
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	198 comment) terminates a multi-line statement.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	199
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	200
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	201 .. _indentation:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	202
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	203 Indentation
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	204 -----------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	205
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	206 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	207 single: indentation
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	208 single: whitespace
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	209 single: leading whitespace
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	210 single: space
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	211 single: tab
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	212 single: grouping
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	213 single: statement grouping
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	214
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	215 Leading whitespace (spaces and tabs) at the beginning of a logical line is used
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	216 to compute the indentation level of the line, which in turn is used to determine
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	217 the grouping of statements.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	218
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	219 First, tabs are replaced (from left to right) by one to eight spaces such that
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	220 the total number of characters up to and including the replacement is a multiple
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	221 of eight (this is intended to be the same rule as used by Unix). The total
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	222 number of spaces preceding the first non-blank character then determines the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	223 line's indentation. Indentation cannot be split over multiple physical lines
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	224 using backslashes; the whitespace up to the first backslash determines the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	225 indentation.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	226
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	227 Cross-platform compatibility note: because of the nature of text editors on
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	228 non-UNIX platforms, it is unwise to use a mixture of spaces and tabs for the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	229 indentation in a single source file. It should also be noted that different
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	230 platforms may explicitly limit the maximum indentation level.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	231
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	232 A formfeed character may be present at the start of the line; it will be ignored
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	233 for the indentation calculations above. Formfeed characters occurring elsewhere
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	234 in the leading whitespace have an undefined effect (for instance, they may reset
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	235 the space count to zero).
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	236
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	237 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	238 single: INDENT token
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	239 single: DEDENT token
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	240
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	241 The indentation levels of consecutive lines are used to generate INDENT and
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	242 DEDENT tokens, using a stack, as follows.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	243
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	244 Before the first line of the file is read, a single zero is pushed on the stack;
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	245 this will never be popped off again. The numbers pushed on the stack will
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	246 always be strictly increasing from bottom to top. At the beginning of each
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	247 logical line, the line's indentation level is compared to the top of the stack.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	248 If it is equal, nothing happens. If it is larger, it is pushed on the stack, and
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	249 one INDENT token is generated. If it is smaller, it must be one of the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	250 numbers occurring on the stack; all numbers on the stack that are larger are
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	251 popped off, and for each number popped off a DEDENT token is generated. At the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	252 end of the file, a DEDENT token is generated for each number remaining on the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	253 stack that is larger than zero.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	254
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	255 Here is an example of a correctly (though confusingly) indented piece of Python
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	256 code::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	257
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	258 def perm(l):
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	259 # Compute the list of all permutations of l
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	260 if len(l) <= 1:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	261 return [l]
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	262 r = []
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	263 for i in range(len(l)):
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	264 s = l[:i] + l[i+1:]
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	265 p = perm(s)
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	266 for x in p:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	267 r.append(l[i:i+1] + x)
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	268 return r
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	269
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	270 The following example shows various indentation errors::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	271
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	272 def perm(l): # error: first line indented
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	273 for i in range(len(l)): # error: not indented
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	274 s = l[:i] + l[i+1:]
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	275 p = perm(l[:i] + l[i+1:]) # error: unexpected indent
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	276 for x in p:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	277 r.append(l[i:i+1] + x)
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	278 return r # error: inconsistent dedent
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	279
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	280 (Actually, the first three errors are detected by the parser; only the last
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	281 error is found by the lexical analyzer --- the indentation of ``return r`` does
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	282 not match a level popped off the stack.)
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	283
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	284
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	285 .. _whitespace:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	286
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	287 Whitespace between tokens
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	288 -------------------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	289
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	290 Except at the beginning of a logical line or in string literals, the whitespace
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	291 characters space, tab and formfeed can be used interchangeably to separate
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	292 tokens. Whitespace is needed between two tokens only if their concatenation
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	293 could otherwise be interpreted as a different token (e.g., ab is one token, but
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	294 a b is two tokens).
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	295
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	296
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	297 .. _other-tokens:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	298
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	299 Other tokens
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	300 ============
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	301
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	302 Besides NEWLINE, INDENT and DEDENT, the following categories of tokens exist:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	303 identifiers, keywords, literals, operators, and delimiters. Whitespace
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	304 characters (other than line terminators, discussed earlier) are not tokens, but
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	305 serve to delimit tokens. Where ambiguity exists, a token comprises the longest
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	306 possible string that forms a legal token, when read from left to right.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	307
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	308
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	309 .. _identifiers:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	310
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	311 Identifiers and keywords
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	312 ========================
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	313
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	314 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	315 single: identifier
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	316 single: name
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	317
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	318 Identifiers (also referred to as names) are described by the following lexical
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	319 definitions:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	320
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	321 .. productionlist::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	322 identifier: (`letter`\|"_") (`letter` \| `digit` \| "_")*
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	323 letter: `lowercase` \| `uppercase`
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	324 lowercase: "a"..."z"
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	325 uppercase: "A"..."Z"
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	326 digit: "0"..."9"
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	327
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	328 Identifiers are unlimited in length. Case is significant.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	329
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	330
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	331 .. _keywords:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	332
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	333 Keywords
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	334 --------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	335
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	336 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	337 single: keyword
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	338 single: reserved word
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	339
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	340 The following identifiers are used as reserved words, or keywords of the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	341 language, and cannot be used as ordinary identifiers. They must be spelled
54348 a27a739cef7f Merged revisions 72085,72132,72159,72288,72290,72292 via svnmerge from Georg Brandl <georg@python.org> parents: 50522 diff changeset	342 exactly as written here:
a27a739cef7f Merged revisions 72085,72132,72159,72288,72290,72292 via svnmerge from Georg Brandl <georg@python.org> parents: 50522 diff changeset	343
a27a739cef7f Merged revisions 72085,72132,72159,72288,72290,72292 via svnmerge from Georg Brandl <georg@python.org> parents: 50522 diff changeset	344 .. sourcecode:: text
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	345
50522 ee9ced92843a Merged revisions 68133-68134,68141-68142,68145-68146,68148-68149,68159-68162,68166,68171-68174,68179,68195-68196,68210,68214-68215,68217-68222 via svnmerge from Georg Brandl <georg@python.org> parents: 49619 diff changeset	346 and del from not while
ee9ced92843a Merged revisions 68133-68134,68141-68142,68145-68146,68148-68149,68159-68162,68166,68171-68174,68179,68195-68196,68210,68214-68215,68217-68222 via svnmerge from Georg Brandl <georg@python.org> parents: 49619 diff changeset	347 as elif global or with
ee9ced92843a Merged revisions 68133-68134,68141-68142,68145-68146,68148-68149,68159-68162,68166,68171-68174,68179,68195-68196,68210,68214-68215,68217-68222 via svnmerge from Georg Brandl <georg@python.org> parents: 49619 diff changeset	348 assert else if pass yield
ee9ced92843a Merged revisions 68133-68134,68141-68142,68145-68146,68148-68149,68159-68162,68166,68171-68174,68179,68195-68196,68210,68214-68215,68217-68222 via svnmerge from Georg Brandl <georg@python.org> parents: 49619 diff changeset	349 break except import print
ee9ced92843a Merged revisions 68133-68134,68141-68142,68145-68146,68148-68149,68159-68162,68166,68171-68174,68179,68195-68196,68210,68214-68215,68217-68222 via svnmerge from Georg Brandl <georg@python.org> parents: 49619 diff changeset	350 class exec in raise
ee9ced92843a Merged revisions 68133-68134,68141-68142,68145-68146,68148-68149,68159-68162,68166,68171-68174,68179,68195-68196,68210,68214-68215,68217-68222 via svnmerge from Georg Brandl <georg@python.org> parents: 49619 diff changeset	351 continue finally is return
ee9ced92843a Merged revisions 68133-68134,68141-68142,68145-68146,68148-68149,68159-68162,68166,68171-68174,68179,68195-68196,68210,68214-68215,68217-68222 via svnmerge from Georg Brandl <georg@python.org> parents: 49619 diff changeset	352 def for lambda try
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	353
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	354 .. versionchanged:: 2.4
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	355 :const:`None` became a constant and is now recognized by the compiler as a name
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	356 for the built-in object :const:`None`. Although it is not a keyword, you cannot
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	357 assign a different object to it.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	358
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	359 .. versionchanged:: 2.5
74550 c84b39c18963 Issue13820 as and with really became keywords in 2.6. Terry Jan Reedy <tjreedy@udel.edu> parents: 68256 diff changeset	360 Using :keyword:`as` and :keyword:`with` as identifiers triggers a warning. To
c84b39c18963 Issue13820 as and with really became keywords in 2.6. Terry Jan Reedy <tjreedy@udel.edu> parents: 68256 diff changeset	361 use them as keywords, enable the ``with_statement`` future feature .
74551 117d58fc6e8d whitespace Terry Jan Reedy <tjreedy@udel.edu> parents: 74550 diff changeset	362
74550 c84b39c18963 Issue13820 as and with really became keywords in 2.6. Terry Jan Reedy <tjreedy@udel.edu> parents: 68256 diff changeset	363 .. versionchanged:: 2.6
c84b39c18963 Issue13820 as and with really became keywords in 2.6. Terry Jan Reedy <tjreedy@udel.edu> parents: 68256 diff changeset	364 :keyword:`as` and :keyword:`with` are full keywords.
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	365
74551 117d58fc6e8d whitespace Terry Jan Reedy <tjreedy@udel.edu> parents: 74550 diff changeset	366
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	367 .. _id-classes:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	368
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	369 Reserved classes of identifiers
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	370 -------------------------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	371
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	372 Certain classes of identifiers (besides keywords) have special meanings. These
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	373 classes are identified by the patterns of leading and trailing underscore
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	374 characters:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	375
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	376 ``_*``
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	377 Not imported by ``from module import *``. The special identifier ``_`` is used
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	378 in the interactive interpreter to store the result of the last evaluation; it is
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	379 stored in the :mod:`__builtin__` module. When not in interactive mode, ``_``
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	380 has no special meaning and is not defined. See section :ref:`import`.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	381
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	382 .. note::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	383
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	384 The name ``_`` is often used in conjunction with internationalization;
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	385 refer to the documentation for the :mod:`gettext` module for more
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	386 information on this convention.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	387
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	388 ``__*__``
63609 a9cd2550ff40 Merged revisions 83593 via svnmerge from Georg Brandl <georg@python.org> parents: 54348 diff changeset	389 System-defined names. These names are defined by the interpreter and its
a9cd2550ff40 Merged revisions 83593 via svnmerge from Georg Brandl <georg@python.org> parents: 54348 diff changeset	390 implementation (including the standard library). Current system names are
a9cd2550ff40 Merged revisions 83593 via svnmerge from Georg Brandl <georg@python.org> parents: 54348 diff changeset	391 discussed in the :ref:`specialnames` section and elsewhere. More will likely
a9cd2550ff40 Merged revisions 83593 via svnmerge from Georg Brandl <georg@python.org> parents: 54348 diff changeset	392 be defined in future versions of Python. Any use of ``__*__`` names, in
a9cd2550ff40 Merged revisions 83593 via svnmerge from Georg Brandl <georg@python.org> parents: 54348 diff changeset	393 any context, that does not follow explicitly documented use, is subject to
a9cd2550ff40 Merged revisions 83593 via svnmerge from Georg Brandl <georg@python.org> parents: 54348 diff changeset	394 breakage without warning.
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	395
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	396 ``__*``
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	397 Class-private names. Names in this category, when used within the context of a
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	398 class definition, are re-written to use a mangled form to help avoid name
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	399 clashes between "private" attributes of base and derived classes. See section
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	400 :ref:`atom-identifiers`.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	401
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	402
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	403 .. _literals:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	404
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	405 Literals
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	406 ========
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	407
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	408 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	409 single: literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	410 single: constant
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	411
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	412 Literals are notations for constant values of some built-in types.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	413
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	414
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	415 .. _strings:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	416
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	417 String literals
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	418 ---------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	419
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	420 .. index:: single: string literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	421
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	422 String literals are described by the following lexical definitions:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	423
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	424 .. index:: single: ASCII@ASCII
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	425
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	426 .. productionlist::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	427 stringliteral: [`stringprefix`](`shortstring` \| `longstring`)
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	428 stringprefix: "r" \| "u" \| "ur" \| "R" \| "U" \| "UR" \| "Ur" \| "uR"
64939 6511165e4830 #1865: document syntax for bytes literals. Georg Brandl <georg@python.org> parents: 63608 diff changeset	429 : \| "b" \| "B" \| "br" \| "Br" \| "bR" \| "BR"
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	430 shortstring: "'" `shortstringitem`* "'" \| '"' `shortstringitem`* '"'
48186 236637390457 Fix longstringitem definition. #3505. Georg Brandl <georg@python.org> parents: 44872 diff changeset	431 longstring: "'''" `longstringitem`* "'''"
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	432 : \| '"""' `longstringitem`* '"""'
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	433 shortstringitem: `shortstringchar` \| `escapeseq`
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	434 longstringitem: `longstringchar` \| `escapeseq`
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	435 shortstringchar: <any source character except "\" or newline or the quote>
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	436 longstringchar: <any source character except "\">
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	437 escapeseq: "\" <any ASCII character>
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	438
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	439 One syntactic restriction not indicated by these productions is that whitespace
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	440 is not allowed between the :token:`stringprefix` and the rest of the string
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	441 literal. The source character set is defined by the encoding declaration; it is
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	442 ASCII if no encoding declaration is given in the source file; see section
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	443 :ref:`encodings`.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	444
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	445 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	446 single: triple-quoted string
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	447 single: Unicode Consortium
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	448 single: string; Unicode
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	449 single: raw string
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	450
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	451 In plain English: String literals can be enclosed in matching single quotes
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	452 (``'``) or double quotes (``"``). They can also be enclosed in matching groups
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	453 of three single or double quotes (these are generally referred to as
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	454 triple-quoted strings). The backslash (``\``) character is used to escape
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	455 characters that otherwise have a special meaning, such as newline, backslash
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	456 itself, or the quote character. String literals may optionally be prefixed with
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	457 a letter ``'r'`` or ``'R'``; such strings are called :dfn:`raw strings` and use
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	458 different rules for interpreting backslash escape sequences. A prefix of
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	459 ``'u'`` or ``'U'`` makes the string a Unicode string. Unicode strings use the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	460 Unicode character set as defined by the Unicode Consortium and ISO 10646. Some
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	461 additional escape sequences, described below, are available in Unicode strings.
64939 6511165e4830 #1865: document syntax for bytes literals. Georg Brandl <georg@python.org> parents: 63608 diff changeset	462 A prefix of ``'b'`` or ``'B'`` is ignored in Python 2; it indicates that the
6511165e4830 #1865: document syntax for bytes literals. Georg Brandl <georg@python.org> parents: 63608 diff changeset	463 literal should become a bytes literal in Python 3 (e.g. when code is
6511165e4830 #1865: document syntax for bytes literals. Georg Brandl <georg@python.org> parents: 63608 diff changeset	464 automatically converted with 2to3). A ``'u'`` or ``'b'`` prefix may be followed
6511165e4830 #1865: document syntax for bytes literals. Georg Brandl <georg@python.org> parents: 63608 diff changeset	465 by an ``'r'`` prefix.
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	466
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	467 In triple-quoted strings, unescaped newlines and quotes are allowed (and are
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	468 retained), except that three unescaped quotes in a row terminate the string. (A
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	469 "quote" is the character used to open the string, i.e. either ``'`` or ``"``.)
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	470
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	471 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	472 single: physical line
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	473 single: escape sequence
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	474 single: Standard C
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	475 single: C
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	476
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	477 Unless an ``'r'`` or ``'R'`` prefix is present, escape sequences in strings are
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	478 interpreted according to rules similar to those used by Standard C. The
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	479 recognized escape sequences are:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	480
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	481 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	482 \| Escape Sequence \| Meaning \| Notes \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	483 +=================+=================================+=======+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	484 \| ``\newline`` \| Ignored \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	485 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	486 \| ``\\`` \| Backslash (``\``) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	487 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	488 \| ``\'`` \| Single quote (``'``) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	489 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	490 \| ``\"`` \| Double quote (``"``) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	491 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	492 \| ``\a`` \| ASCII Bell (BEL) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	493 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	494 \| ``\b`` \| ASCII Backspace (BS) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	495 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	496 \| ``\f`` \| ASCII Formfeed (FF) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	497 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	498 \| ``\n`` \| ASCII Linefeed (LF) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	499 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	500 \| ``\N{name}`` \| Character named name in the \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	501 \| \| Unicode database (Unicode only) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	502 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	503 \| ``\r`` \| ASCII Carriage Return (CR) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	504 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	505 \| ``\t`` \| ASCII Horizontal Tab (TAB) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	506 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	507 \| ``\uxxxx`` \| Character with 16-bit hex value \| \(1) \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	508 \| \| xxxx (Unicode only) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	509 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	510 \| ``\Uxxxxxxxx`` \| Character with 32-bit hex value \| \(2) \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	511 \| \| xxxxxxxx (Unicode only) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	512 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	513 \| ``\v`` \| ASCII Vertical Tab (VT) \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	514 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	515 \| ``\ooo`` \| Character with octal value \| (3,5) \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	516 \| \| ooo \| \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	517 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	518 \| ``\xhh`` \| Character with hex value hh \| (4,5) \|
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	519 +-----------------+---------------------------------+-------+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	520
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	521 .. index:: single: ASCII@ASCII
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	522
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	523 Notes:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	524
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	525 (1)
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	526 Individual code units which form parts of a surrogate pair can be encoded using
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	527 this escape sequence.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	528
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	529 (2)
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	530 Any Unicode character can be encoded this way, but characters outside the Basic
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	531 Multilingual Plane (BMP) will be encoded using a surrogate pair if Python is
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	532 compiled to use 16-bit code units (the default). Individual code units which
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	533 form parts of a surrogate pair can be encoded using this escape sequence.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	534
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	535 (3)
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	536 As in Standard C, up to three octal digits are accepted.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	537
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	538 (4)
44872 12b6910115e0 Fix \xhh specs, #1889. Georg Brandl <georg@python.org> parents: 44383 diff changeset	539 Unlike in Standard C, exactly two hex digits are required.
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	540
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	541 (5)
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	542 In a string literal, hexadecimal and octal escapes denote the byte with the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	543 given value; it is not necessary that the byte encodes a character in the source
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	544 character set. In a Unicode literal, these escapes denote a Unicode character
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	545 with the given value.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	546
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	547 .. index:: single: unrecognized escape sequence
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	548
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	549 Unlike Standard C, all unrecognized escape sequences are left in the string
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	550 unchanged, i.e., the backslash is left in the string. (This behavior is
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	551 useful when debugging: if an escape sequence is mistyped, the resulting output
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	552 is more easily recognized as broken.) It is also important to note that the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	553 escape sequences marked as "(Unicode only)" in the table above fall into the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	554 category of unrecognized escapes for non-Unicode string literals.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	555
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	556 When an ``'r'`` or ``'R'`` prefix is present, a character following a backslash
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	557 is included in the string without change, and *all backslashes are left in the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	558 string*. For example, the string literal ``r"\n"`` consists of two characters:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	559 a backslash and a lowercase ``'n'``. String quotes can be escaped with a
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	560 backslash, but the backslash remains in the string; for example, ``r"\""`` is a
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	561 valid string literal consisting of two characters: a backslash and a double
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	562 quote; ``r"\"`` is not a valid string literal (even a raw string cannot end in
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	563 an odd number of backslashes). Specifically, *a raw string cannot end in a
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	564 single backslash* (since the backslash would escape the following quote
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	565 character). Note also that a single backslash followed by a newline is
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	566 interpreted as those two characters as part of the string, not as a line
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	567 continuation.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	568
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	569 When an ``'r'`` or ``'R'`` prefix is used in conjunction with a ``'u'`` or
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	570 ``'U'`` prefix, then the ``\uXXXX`` and ``\UXXXXXXXX`` escape sequences are
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	571 processed while all other backslashes are left in the string. For example,
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	572 the string literal ``ur"\u0062\n"`` consists of three Unicode characters: 'LATIN
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	573 SMALL LETTER B', 'REVERSE SOLIDUS', and 'LATIN SMALL LETTER N'. Backslashes can
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	574 be escaped with a preceding backslash; however, both remain in the string. As a
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	575 result, ``\uXXXX`` escape sequences are only recognized when there are an odd
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	576 number of backslashes.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	577
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	578
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	579 .. _string-catenation:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	580
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	581 String literal concatenation
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	582 ----------------------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	583
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	584 Multiple adjacent string literals (delimited by whitespace), possibly using
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	585 different quoting conventions, are allowed, and their meaning is the same as
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	586 their concatenation. Thus, ``"hello" 'world'`` is equivalent to
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	587 ``"helloworld"``. This feature can be used to reduce the number of backslashes
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	588 needed, to split long strings conveniently across long lines, or even to add
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	589 comments to parts of strings, for example::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	590
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	591 re.compile("[A-Za-z_]" # letter or underscore
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	592 "[A-Za-z0-9_]*" # letter, digit or underscore
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	593 )
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	594
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	595 Note that this feature is defined at the syntactical level, but implemented at
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	596 compile time. The '+' operator must be used to concatenate string expressions
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	597 at run time. Also note that literal concatenation can use different quoting
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	598 styles for each component (even mixing raw strings and triple quoted strings).
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	599
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	600
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	601 .. _numbers:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	602
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	603 Numeric literals
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	604 ----------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	605
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	606 .. index::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	607 single: number
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	608 single: numeric literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	609 single: integer literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	610 single: plain integer literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	611 single: long integer literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	612 single: floating point literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	613 single: hexadecimal literal
49619 06cf2cea387b Merged revisions 67060-67061 via svnmerge from Benjamin Peterson <benjamin@python.org> parents: 49184 diff changeset	614 single: binary literal
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	615 single: octal literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	616 single: decimal literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	617 single: imaginary literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	618 single: complex; literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	619
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	620 There are four types of numeric literals: plain integers, long integers,
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	621 floating point numbers, and imaginary numbers. There are no complex literals
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	622 (complex numbers can be formed by adding a real number and an imaginary number).
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	623
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	624 Note that numeric literals do not include a sign; a phrase like ``-1`` is
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	625 actually an expression composed of the unary operator '``-``' and the literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	626 ``1``.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	627
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	628
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	629 .. _integers:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	630
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	631 Integer and long integer literals
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	632 ---------------------------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	633
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	634 Integer and long integer literals are described by the following lexical
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	635 definitions:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	636
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	637 .. productionlist::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	638 longinteger: `integer` ("l" \| "L")
49619 06cf2cea387b Merged revisions 67060-67061 via svnmerge from Benjamin Peterson <benjamin@python.org> parents: 49184 diff changeset	639 integer: `decimalinteger` \| `octinteger` \| `hexinteger` \| `bininteger`
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	640 decimalinteger: `nonzerodigit` `digit`* \| "0"
49619 06cf2cea387b Merged revisions 67060-67061 via svnmerge from Benjamin Peterson <benjamin@python.org> parents: 49184 diff changeset	641 octinteger: "0" ("o" \| "O") `octdigit`+ \| "0" `octdigit`+
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	642 hexinteger: "0" ("x" \| "X") `hexdigit`+
49619 06cf2cea387b Merged revisions 67060-67061 via svnmerge from Benjamin Peterson <benjamin@python.org> parents: 49184 diff changeset	643 bininteger: "0" ("b" \| "B") `bindigit`+
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	644 nonzerodigit: "1"..."9"
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	645 octdigit: "0"..."7"
49619 06cf2cea387b Merged revisions 67060-67061 via svnmerge from Benjamin Peterson <benjamin@python.org> parents: 49184 diff changeset	646 bindigit: "0" \| "1"
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	647 hexdigit: `digit` \| "a"..."f" \| "A"..."F"
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	648
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	649 Although both lower case ``'l'`` and upper case ``'L'`` are allowed as suffix
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	650 for long integers, it is strongly recommended to always use ``'L'``, since the
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	651 letter ``'l'`` looks too much like the digit ``'1'``.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	652
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	653 Plain integer literals that are above the largest representable plain integer
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	654 (e.g., 2147483647 when using 32-bit arithmetic) are accepted as if they were
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	655 long integers instead. [#]_ There is no limit for long integer literals apart
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	656 from what can be stored in available memory.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	657
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	658 Some examples of plain integer literals (first row) and long integer literals
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	659 (second and third rows)::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	660
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	661 7 2147483647 0177
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	662 3L 79228162514264337593543950336L 0377L 0x100000000L
50522 ee9ced92843a Merged revisions 68133-68134,68141-68142,68145-68146,68148-68149,68159-68162,68166,68171-68174,68179,68195-68196,68210,68214-68215,68217-68222 via svnmerge from Georg Brandl <georg@python.org> parents: 49619 diff changeset	663 79228162514264337593543950336 0xdeadbeef
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	664
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	665
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	666 .. _floating:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	667
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	668 Floating point literals
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	669 -----------------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	670
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	671 Floating point literals are described by the following lexical definitions:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	672
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	673 .. productionlist::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	674 floatnumber: `pointfloat` \| `exponentfloat`
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	675 pointfloat: [`intpart`] `fraction` \| `intpart` "."
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	676 exponentfloat: (`intpart` \| `pointfloat`) `exponent`
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	677 intpart: `digit`+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	678 fraction: "." `digit`+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	679 exponent: ("e" \| "E") ["+" \| "-"] `digit`+
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	680
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	681 Note that the integer and exponent parts of floating point numbers can look like
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	682 octal integers, but are interpreted using radix 10. For example, ``077e010`` is
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	683 legal, and denotes the same number as ``77e10``. The allowed range of floating
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	684 point literals is implementation-dependent. Some examples of floating point
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	685 literals::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	686
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	687 3.14 10. .001 1e100 3.14e-10 0e0
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	688
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	689 Note that numeric literals do not include a sign; a phrase like ``-1`` is
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	690 actually an expression composed of the unary operator ``-`` and the literal
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	691 ``1``.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	692
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	693
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	694 .. _imaginary:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	695
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	696 Imaginary literals
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	697 ------------------
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	698
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	699 Imaginary literals are described by the following lexical definitions:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	700
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	701 .. productionlist::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	702 imagnumber: (`floatnumber` \| `intpart`) ("j" \| "J")
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	703
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	704 An imaginary literal yields a complex number with a real part of 0.0. Complex
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	705 numbers are represented as a pair of floating point numbers and have the same
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	706 restrictions on their range. To create a complex number with a nonzero real
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	707 part, add a floating point number to it, e.g., ``(3+4j)``. Some examples of
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	708 imaginary literals::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	709
50522 ee9ced92843a Merged revisions 68133-68134,68141-68142,68145-68146,68148-68149,68159-68162,68166,68171-68174,68179,68195-68196,68210,68214-68215,68217-68222 via svnmerge from Georg Brandl <georg@python.org> parents: 49619 diff changeset	710 3.14j 10.j 10j .001j 1e100j 3.14e-10j
42603 c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	711
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	712
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	713 .. _operators:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	714
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	715 Operators
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	716 =========
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	717
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	718 .. index:: single: operators
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	719
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	720 The following tokens are operators::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	721
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	722 + - * ** / // %
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	723 << >> & \| ^ ~
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	724 < > <= >= == != <>
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	725
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	726 The comparison operators ``<>`` and ``!=`` are alternate spellings of the same
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	727 operator. ``!=`` is the preferred spelling; ``<>`` is obsolescent.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	728
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	729
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	730 .. _delimiters:
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	731
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	732 Delimiters
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	733 ==========
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	734
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	735 .. index:: single: delimiters
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	736
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	737 The following tokens serve as delimiters in the grammar::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	738
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	739 ( ) [ ] { } @
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	740 , : . ` = ;
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	741 += -= *= /= //= %=
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	742 &= \|= ^= >>= <<= **=
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	743
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	744 The period can also occur in floating-point and imaginary literals. A sequence
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	745 of three periods has a special meaning as an ellipsis in slices. The second half
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	746 of the list, the augmented assignment operators, serve lexically as delimiters,
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	747 but also perform an operation.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	748
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	749 The following printing ASCII characters have special meaning as part of other
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	750 tokens or are otherwise significant to the lexical analyzer::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	751
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	752 ' " # \
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	753
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	754 .. index:: single: ASCII@ASCII
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	755
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	756 The following printing ASCII characters are not used in Python. Their
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	757 occurrence outside string literals and comments is an unconditional error::
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	758
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	759 $ ?
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	760
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	761 .. rubric:: Footnotes
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	762
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	763 .. [#] In versions of Python prior to 2.4, octal and hexadecimal literals in the range
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	764 just above the largest representable plain integer but below the largest
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	765 unsigned 32-bit number (on a machine using 32-bit arithmetic), 4294967296, were
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	766 taken as the negative plain integer obtained by subtracting 4294967296 from
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	767 their unsigned value.
c62f6669ae22 Move the 2.6 reST doc tree in place. Georg Brandl <georg@python.org> parents: diff changeset	768

Mercurial > cpython-lru_cache-weakref

annotate Doc/reference/lexical_analysis.rst @ 79675:c0a2294de787 2.7