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author Johannes Gijsbers <jlg@dds.nl>
date Mon, 13 Dec 2004 13:11:42 +0000
parents 2fa872784eb6
children 67f2190e1f6d
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1 \section{\module{difflib} ---
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2 Helpers for computing deltas}
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3
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4 \declaremodule{standard}{difflib}
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5 \modulesynopsis{Helpers for computing differences between objects.}
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6 \moduleauthor{Tim Peters}{tim_one@users.sourceforge.net}
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7 \sectionauthor{Tim Peters}{tim_one@users.sourceforge.net}
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8 % LaTeXification by Fred L. Drake, Jr. <fdrake@acm.org>.
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9
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10 \versionadded{2.1}
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12
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13 \begin{classdesc*}{SequenceMatcher}
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14 This is a flexible class for comparing pairs of sequences of any
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15 type, so long as the sequence elements are hashable. The basic
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16 algorithm predates, and is a little fancier than, an algorithm
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17 published in the late 1980's by Ratcliff and Obershelp under the
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18 hyperbolic name ``gestalt pattern matching.'' The idea is to find
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19 the longest contiguous matching subsequence that contains no
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20 ``junk'' elements (the Ratcliff and Obershelp algorithm doesn't
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21 address junk). The same idea is then applied recursively to the
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22 pieces of the sequences to the left and to the right of the matching
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23 subsequence. This does not yield minimal edit sequences, but does
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24 tend to yield matches that ``look right'' to people.
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25
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26 \strong{Timing:} The basic Ratcliff-Obershelp algorithm is cubic
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27 time in the worst case and quadratic time in the expected case.
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28 \class{SequenceMatcher} is quadratic time for the worst case and has
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29 expected-case behavior dependent in a complicated way on how many
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30 elements the sequences have in common; best case time is linear.
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31 \end{classdesc*}
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32
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33 \begin{classdesc*}{Differ}
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34 This is a class for comparing sequences of lines of text, and
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35 producing human-readable differences or deltas. Differ uses
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36 \class{SequenceMatcher} both to compare sequences of lines, and to
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37 compare sequences of characters within similar (near-matching)
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38 lines.
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39
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40 Each line of a \class{Differ} delta begins with a two-letter code:
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41
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42 \begin{tableii}{l|l}{code}{Code}{Meaning}
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43 \lineii{'- '}{line unique to sequence 1}
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44 \lineii{'+ '}{line unique to sequence 2}
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45 \lineii{' '}{line common to both sequences}
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46 \lineii{'? '}{line not present in either input sequence}
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47 \end{tableii}
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48
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49 Lines beginning with `\code{?~}' attempt to guide the eye to
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50 intraline differences, and were not present in either input
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51 sequence. These lines can be confusing if the sequences contain tab
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52 characters.
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53 \end{classdesc*}
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54
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55 \begin{classdesc*}{HtmlDiff}
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57 This class can be used to create an HTML table (or a complete HTML file
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58 containing the table) showing a side by side, line by line comparison
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59 of text with inter-line and intra-line change highlights. The table can
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60 be generated in either full or contextual difference mode.
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61
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62 The constructor for this class is:
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63
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64 \begin{funcdesc}{__init__}{\optional{tabsize}\optional{,
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65 wrapcolumn}\optional{, linejunk}\optional{, charjunk}}
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66
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67 Initializes instance of \class{HtmlDiff}.
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68
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69 \var{tabsize} is an optional keyword argument to specify tab stop spacing
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70 and defaults to \code{8}.
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71
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72 \var{wrapcolumn} is an optional keyword to specify column number where
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73 lines are broken and wrapped, defaults to \code{None} where lines are not
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74 wrapped.
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76 \var{linejunk} and \var{charjunk} are optional keyword arguments passed
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77 into \code{ndiff()} (used by \class{HtmlDiff} to generate the
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78 side by side HTML differences). See \code{ndiff()} documentation for
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79 argument default values and descriptions.
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80
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81 \end{funcdesc}
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82
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83 The following methods are public:
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84
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85 \begin{funcdesc}{make_file}{fromlines, tolines
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86 \optional{, fromdesc}\optional{, todesc}\optional{, context}\optional{,
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87 numlines}}
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88 Compares \var{fromlines} and \var{tolines} (lists of strings) and returns
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89 a string which is a complete HTML file containing a table showing line by
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90 line differences with inter-line and intra-line changes highlighted.
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91
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92 \var{fromdesc} and \var{todesc} are optional keyword arguments to specify
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93 from/to file column header strings (both default to an empty string).
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94
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95 \var{context} and \var{numlines} are both optional keyword arguments.
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96 Set \var{context} to \code{True} when contextual differences are to be
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97 shown, else the default is \code{False} to show the full files.
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98 \var{numlines} defaults to \code{5}. When \var{context} is \code{True}
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99 \var{numlines} controls the number of context lines which surround the
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100 difference highlights. When \var{context} is \code{False} \var{numlines}
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101 controls the number of lines which are shown before a difference
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102 highlight when using the "next" hyperlinks (setting to zero would cause
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103 the "next" hyperlinks to place the next difference highlight at the top of
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104 the browser without any leading context).
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105 \end{funcdesc}
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106
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107 \begin{funcdesc}{make_table}{fromlines, tolines
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108 \optional{, fromdesc}\optional{, todesc}\optional{, context}\optional{,
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109 numlines}}
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110 Compares \var{fromlines} and \var{tolines} (lists of strings) and returns
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111 a string which is a complete HTML table showing line by line differences
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112 with inter-line and intra-line changes highlighted.
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113
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114 The arguments for this method are the same as those for the
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115 \method{make_file()} method.
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116 \end{funcdesc}
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117
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118 \file{Tools/scripts/diff.py} is a command-line front-end to this class
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119 and contains a good example of its use.
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120
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121 \versionadded{2.4}
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122 \end{classdesc*}
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123
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124 \begin{funcdesc}{context_diff}{a, b\optional{, fromfile}\optional{,
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125 tofile}\optional{, fromfiledate}\optional{, tofiledate}\optional{,
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126 n}\optional{, lineterm}}
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127 Compare \var{a} and \var{b} (lists of strings); return a
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128 delta (a generator generating the delta lines) in context diff
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129 format.
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130
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131 Context diffs are a compact way of showing just the lines that have
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132 changed plus a few lines of context. The changes are shown in a
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133 before/after style. The number of context lines is set by \var{n}
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134 which defaults to three.
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135
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136 By default, the diff control lines (those with \code{***} or \code{---})
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137 are created with a trailing newline. This is helpful so that inputs created
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138 from \function{file.readlines()} result in diffs that are suitable for use
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139 with \function{file.writelines()} since both the inputs and outputs have
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140 trailing newlines.
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141
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142 For inputs that do not have trailing newlines, set the \var{lineterm}
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143 argument to \code{""} so that the output will be uniformly newline free.
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144
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145 The context diff format normally has a header for filenames and
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146 modification times. Any or all of these may be specified using strings for
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147 \var{fromfile}, \var{tofile}, \var{fromfiledate}, and \var{tofiledate}.
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148 The modification times are normally expressed in the format returned by
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149 \function{time.ctime()}. If not specified, the strings default to blanks.
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150
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151 \file{Tools/scripts/diff.py} is a command-line front-end for this
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152 function.
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153
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154 \versionadded{2.3}
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155 \end{funcdesc}
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156
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157 \begin{funcdesc}{get_close_matches}{word, possibilities\optional{,
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158 n}\optional{, cutoff}}
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159 Return a list of the best ``good enough'' matches. \var{word} is a
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160 sequence for which close matches are desired (typically a string),
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161 and \var{possibilities} is a list of sequences against which to
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162 match \var{word} (typically a list of strings).
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163
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164 Optional argument \var{n} (default \code{3}) is the maximum number
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165 of close matches to return; \var{n} must be greater than \code{0}.
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166
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167 Optional argument \var{cutoff} (default \code{0.6}) is a float in
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168 the range [0, 1]. Possibilities that don't score at least that
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169 similar to \var{word} are ignored.
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170
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171 The best (no more than \var{n}) matches among the possibilities are
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172 returned in a list, sorted by similarity score, most similar first.
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173
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174 \begin{verbatim}
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175 >>> get_close_matches('appel', ['ape', 'apple', 'peach', 'puppy'])
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176 ['apple', 'ape']
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177 >>> import keyword
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178 >>> get_close_matches('wheel', keyword.kwlist)
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179 ['while']
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180 >>> get_close_matches('apple', keyword.kwlist)
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181 []
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182 >>> get_close_matches('accept', keyword.kwlist)
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183 ['except']
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184 \end{verbatim}
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185 \end{funcdesc}
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186
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187 \begin{funcdesc}{ndiff}{a, b\optional{, linejunk}\optional{, charjunk}}
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188 Compare \var{a} and \var{b} (lists of strings); return a
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189 \class{Differ}-style delta (a generator generating the delta lines).
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190
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191 Optional keyword parameters \var{linejunk} and \var{charjunk} are
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192 for filter functions (or \code{None}):
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193
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194 \var{linejunk}: A function that accepts a single string
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195 argument, and returns true if the string is junk, or false if not.
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196 The default is (\code{None}), starting with Python 2.3. Before then,
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197 the default was the module-level function
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198 \function{IS_LINE_JUNK()}, which filters out lines without visible
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199 characters, except for at most one pound character (\character{\#}).
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200 As of Python 2.3, the underlying \class{SequenceMatcher} class
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201 does a dynamic analysis of which lines are so frequent as to
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202 constitute noise, and this usually works better than the pre-2.3
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203 default.
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204
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205 \var{charjunk}: A function that accepts a character (a string of
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206 length 1), and returns if the character is junk, or false if not.
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207 The default is module-level function \function{IS_CHARACTER_JUNK()},
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208 which filters out whitespace characters (a blank or tab; note: bad
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209 idea to include newline in this!).
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210
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211 \file{Tools/scripts/ndiff.py} is a command-line front-end to this
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212 function.
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213
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214 \begin{verbatim}
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215 >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(1),
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216 ... 'ore\ntree\nemu\n'.splitlines(1))
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217 >>> print ''.join(diff),
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218 - one
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219 ? ^
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220 + ore
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221 ? ^
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222 - two
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223 - three
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224 ? -
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225 + tree
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226 + emu
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227 \end{verbatim}
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228 \end{funcdesc}
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229
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230 \begin{funcdesc}{restore}{sequence, which}
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231 Return one of the two sequences that generated a delta.
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232
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233 Given a \var{sequence} produced by \method{Differ.compare()} or
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234 \function{ndiff()}, extract lines originating from file 1 or 2
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235 (parameter \var{which}), stripping off line prefixes.
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236
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237 Example:
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238
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239 \begin{verbatim}
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240 >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(1),
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241 ... 'ore\ntree\nemu\n'.splitlines(1))
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242 >>> diff = list(diff) # materialize the generated delta into a list
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243 >>> print ''.join(restore(diff, 1)),
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244 one
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245 two
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246 three
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247 >>> print ''.join(restore(diff, 2)),
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248 ore
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249 tree
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250 emu
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251 \end{verbatim}
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252
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253 \end{funcdesc}
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254
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255 \begin{funcdesc}{unified_diff}{a, b\optional{, fromfile}\optional{,
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256 tofile}\optional{, fromfiledate}\optional{, tofiledate}\optional{,
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257 n}\optional{, lineterm}}
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258 Compare \var{a} and \var{b} (lists of strings); return a
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259 delta (a generator generating the delta lines) in unified diff
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260 format.
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261
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262 Unified diffs are a compact way of showing just the lines that have
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263 changed plus a few lines of context. The changes are shown in a
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264 inline style (instead of separate before/after blocks). The number
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265 of context lines is set by \var{n} which defaults to three.
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266
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267 By default, the diff control lines (those with \code{---}, \code{+++},
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268 or \code{@@}) are created with a trailing newline. This is helpful so
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269 that inputs created from \function{file.readlines()} result in diffs
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270 that are suitable for use with \function{file.writelines()} since both
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271 the inputs and outputs have trailing newlines.
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272
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273 For inputs that do not have trailing newlines, set the \var{lineterm}
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274 argument to \code{""} so that the output will be uniformly newline free.
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275
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276 The context diff format normally has a header for filenames and
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277 modification times. Any or all of these may be specified using strings for
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278 \var{fromfile}, \var{tofile}, \var{fromfiledate}, and \var{tofiledate}.
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279 The modification times are normally expressed in the format returned by
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280 \function{time.ctime()}. If not specified, the strings default to blanks.
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281
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282 \file{Tools/scripts/diff.py} is a command-line front-end for this
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283 function.
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284
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285 \versionadded{2.3}
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286 \end{funcdesc}
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287
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288 \begin{funcdesc}{IS_LINE_JUNK}{line}
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289 Return true for ignorable lines. The line \var{line} is ignorable
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290 if \var{line} is blank or contains a single \character{\#},
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291 otherwise it is not ignorable. Used as a default for parameter
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292 \var{linejunk} in \function{ndiff()} before Python 2.3.
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293 \end{funcdesc}
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294
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295
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296 \begin{funcdesc}{IS_CHARACTER_JUNK}{ch}
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297 Return true for ignorable characters. The character \var{ch} is
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298 ignorable if \var{ch} is a space or tab, otherwise it is not
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299 ignorable. Used as a default for parameter \var{charjunk} in
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300 \function{ndiff()}.
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301 \end{funcdesc}
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302
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303
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304 \begin{seealso}
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305 \seetitle[http://www.ddj.com/documents/s=1103/ddj8807c/]
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306 {Pattern Matching: The Gestalt Approach}{Discussion of a
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307 similar algorithm by John W. Ratcliff and D. E. Metzener.
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308 This was published in
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309 \citetitle[http://www.ddj.com/]{Dr. Dobb's Journal} in
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310 July, 1988.}
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311 \end{seealso}
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312
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313
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314 \subsection{SequenceMatcher Objects \label{sequence-matcher}}
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315
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316 The \class{SequenceMatcher} class has this constructor:
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317
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318 \begin{classdesc}{SequenceMatcher}{\optional{isjunk\optional{,
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319 a\optional{, b}}}}
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320 Optional argument \var{isjunk} must be \code{None} (the default) or
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321 a one-argument function that takes a sequence element and returns
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322 true if and only if the element is ``junk'' and should be ignored.
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323 Passing \code{None} for \var{isjunk} is equivalent to passing
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324 \code{lambda x: 0}; in other words, no elements are ignored. For
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325 example, pass:
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326
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327 \begin{verbatim}
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328 lambda x: x in " \t"
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329 \end{verbatim}
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330
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331 if you're comparing lines as sequences of characters, and don't want
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332 to synch up on blanks or hard tabs.
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333
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334 The optional arguments \var{a} and \var{b} are sequences to be
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335 compared; both default to empty strings. The elements of both
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336 sequences must be hashable.
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337 \end{classdesc}
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338
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339
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340 \class{SequenceMatcher} objects have the following methods:
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341
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342 \begin{methoddesc}{set_seqs}{a, b}
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343 Set the two sequences to be compared.
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344 \end{methoddesc}
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345
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346 \class{SequenceMatcher} computes and caches detailed information about
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347 the second sequence, so if you want to compare one sequence against
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348 many sequences, use \method{set_seq2()} to set the commonly used
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349 sequence once and call \method{set_seq1()} repeatedly, once for each
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350 of the other sequences.
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351
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352 \begin{methoddesc}{set_seq1}{a}
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353 Set the first sequence to be compared. The second sequence to be
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354 compared is not changed.
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355 \end{methoddesc}
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356
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357 \begin{methoddesc}{set_seq2}{b}
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358 Set the second sequence to be compared. The first sequence to be
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359 compared is not changed.
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360 \end{methoddesc}
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361
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362 \begin{methoddesc}{find_longest_match}{alo, ahi, blo, bhi}
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363 Find longest matching block in \code{\var{a}[\var{alo}:\var{ahi}]}
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364 and \code{\var{b}[\var{blo}:\var{bhi}]}.
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365
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366 If \var{isjunk} was omitted or \code{None},
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367 \method{get_longest_match()} returns \code{(\var{i}, \var{j},
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368 \var{k})} such that \code{\var{a}[\var{i}:\var{i}+\var{k}]} is equal
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369 to \code{\var{b}[\var{j}:\var{j}+\var{k}]}, where
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370 \code{\var{alo} <= \var{i} <= \var{i}+\var{k} <= \var{ahi}} and
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371 \code{\var{blo} <= \var{j} <= \var{j}+\var{k} <= \var{bhi}}.
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372 For all \code{(\var{i'}, \var{j'}, \var{k'})} meeting those
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373 conditions, the additional conditions
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374 \code{\var{k} >= \var{k'}},
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375 \code{\var{i} <= \var{i'}},
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376 and if \code{\var{i} == \var{i'}}, \code{\var{j} <= \var{j'}}
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377 are also met.
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378 In other words, of all maximal matching blocks, return one that
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379 starts earliest in \var{a}, and of all those maximal matching blocks
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380 that start earliest in \var{a}, return the one that starts earliest
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381 in \var{b}.
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382
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383 \begin{verbatim}
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384 >>> s = SequenceMatcher(None, " abcd", "abcd abcd")
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385 >>> s.find_longest_match(0, 5, 0, 9)
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386 (0, 4, 5)
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387 \end{verbatim}
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388
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
389 If \var{isjunk} was provided, first the longest matching block is
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
390 determined as above, but with the additional restriction that no
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
391 junk element appears in the block. Then that block is extended as
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
392 far as possible by matching (only) junk elements on both sides.
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
393 So the resulting block never matches on junk except as identical
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
394 junk happens to be adjacent to an interesting match.
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
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diff changeset
395
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
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diff changeset
396 Here's the same example as before, but considering blanks to be junk.
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8172906c6dc8 Improve accuracy. In the .tex file, note the new "% BUG:" comments: an
Tim Peters <tim.peters@gmail.com>
parents: 16682
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397 That prevents \code{' abcd'} from matching the \code{' abcd'} at the
16682
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
398 tail end of the second sequence directly. Instead only the
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
399 \code{'abcd'} can match, and matches the leftmost \code{'abcd'} in
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
400 the second sequence:
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
401
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
402 \begin{verbatim}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
403 >>> s = SequenceMatcher(lambda x: x==" ", " abcd", "abcd abcd")
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
404 >>> s.find_longest_match(0, 5, 0, 9)
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
405 (1, 0, 4)
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
406 \end{verbatim}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
407
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
408 If no blocks match, this returns \code{(\var{alo}, \var{blo}, 0)}.
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
409 \end{methoddesc}
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
410
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
411 \begin{methoddesc}{get_matching_blocks}{}
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
412 Return list of triples describing matching subsequences.
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
413 Each triple is of the form \code{(\var{i}, \var{j}, \var{n})}, and
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
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414 means that \code{\var{a}[\var{i}:\var{i}+\var{n}] ==
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Fred Drake <fdrake@acm.org>
parents:
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415 \var{b}[\var{j}:\var{j}+\var{n}]}. The triples are monotonically
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
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diff changeset
416 increasing in \var{i} and \var{j}.
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
417
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
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418 The last triple is a dummy, and has the value \code{(len(\var{a}),
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
419 len(\var{b}), 0)}. It is the only triple with \code{\var{n} == 0}.
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Fred Drake <fdrake@acm.org>
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420 % Explain why a dummy is used!
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
421
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
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422 \begin{verbatim}
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Fred Drake <fdrake@acm.org>
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423 >>> s = SequenceMatcher(None, "abxcd", "abcd")
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Fred Drake <fdrake@acm.org>
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diff changeset
424 >>> s.get_matching_blocks()
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
425 [(0, 0, 2), (3, 2, 2), (5, 4, 0)]
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Fred Drake <fdrake@acm.org>
parents:
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426 \end{verbatim}
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
427 \end{methoddesc}
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
428
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
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429 \begin{methoddesc}{get_opcodes}{}
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Fred Drake <fdrake@acm.org>
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430 Return list of 5-tuples describing how to turn \var{a} into \var{b}.
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Fred Drake <fdrake@acm.org>
parents:
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431 Each tuple is of the form \code{(\var{tag}, \var{i1}, \var{i2},
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
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432 \var{j1}, \var{j2})}. The first tuple has \code{\var{i1} ==
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Fred Drake <fdrake@acm.org>
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433 \var{j1} == 0}, and remaining tuples have \var{i1} equal to the
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
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434 \var{i2} from the preceeding tuple, and, likewise, \var{j1} equal to
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
435 the previous \var{j2}.
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
436
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
437 The \var{tag} values are strings, with these meanings:
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
438
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
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diff changeset
439 \begin{tableii}{l|l}{code}{Value}{Meaning}
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diff changeset
440 \lineii{'replace'}{\code{\var{a}[\var{i1}:\var{i2}]} should be
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
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441 replaced by \code{\var{b}[\var{j1}:\var{j2}]}.}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
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442 \lineii{'delete'}{\code{\var{a}[\var{i1}:\var{i2}]} should be
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
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443 deleted. Note that \code{\var{j1} == \var{j2}} in
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
444 this case.}
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Fred Drake <fdrake@acm.org>
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diff changeset
445 \lineii{'insert'}{\code{\var{b}[\var{j1}:\var{j2}]} should be
20038
8a6f2ee6eaba Make difflib.ndiff() and difflib.Differ.compare() generators. This
Tim Peters <tim.peters@gmail.com>
parents: 19232
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446 inserted at \code{\var{a}[\var{i1}:\var{i1}]}.
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Fred Drake <fdrake@acm.org>
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447 Note that \code{\var{i1} == \var{i2}} in this
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
448 case.}
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Fred Drake <fdrake@acm.org>
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449 \lineii{'equal'}{\code{\var{a}[\var{i1}:\var{i2}] ==
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parents:
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450 \var{b}[\var{j1}:\var{j2}]} (the sub-sequences are
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
451 equal).}
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
452 \end{tableii}
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Fred Drake <fdrake@acm.org>
parents:
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453
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Fred Drake <fdrake@acm.org>
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diff changeset
454 For example:
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Fred Drake <fdrake@acm.org>
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455
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Fred Drake <fdrake@acm.org>
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456 \begin{verbatim}
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Fred Drake <fdrake@acm.org>
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457 >>> a = "qabxcd"
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Fred Drake <fdrake@acm.org>
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458 >>> b = "abycdf"
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Fred Drake <fdrake@acm.org>
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459 >>> s = SequenceMatcher(None, a, b)
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Fred Drake <fdrake@acm.org>
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diff changeset
460 >>> for tag, i1, i2, j1, j2 in s.get_opcodes():
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Fred Drake <fdrake@acm.org>
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461 ... print ("%7s a[%d:%d] (%s) b[%d:%d] (%s)" %
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Fred Drake <fdrake@acm.org>
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462 ... (tag, i1, i2, a[i1:i2], j1, j2, b[j1:j2]))
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
463 delete a[0:1] (q) b[0:0] ()
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Fred Drake <fdrake@acm.org>
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diff changeset
464 equal a[1:3] (ab) b[0:2] (ab)
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
465 replace a[3:4] (x) b[2:3] (y)
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
466 equal a[4:6] (cd) b[3:5] (cd)
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parents:
diff changeset
467 insert a[6:6] () b[5:6] (f)
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Fred Drake <fdrake@acm.org>
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diff changeset
468 \end{verbatim}
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
469 \end{methoddesc}
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
470
29404
8c5a6853a02a Add docs for get_grouped_opcodes().
Raymond Hettinger <python@rcn.com>
parents: 29398
diff changeset
471 \begin{methoddesc}{get_grouped_opcodes}{\optional{n}}
8c5a6853a02a Add docs for get_grouped_opcodes().
Raymond Hettinger <python@rcn.com>
parents: 29398
diff changeset
472 Return a generator of groups with up to \var{n} lines of context.
8c5a6853a02a Add docs for get_grouped_opcodes().
Raymond Hettinger <python@rcn.com>
parents: 29398
diff changeset
473
8c5a6853a02a Add docs for get_grouped_opcodes().
Raymond Hettinger <python@rcn.com>
parents: 29398
diff changeset
474 Starting with the groups returned by \method{get_opcodes()},
8c5a6853a02a Add docs for get_grouped_opcodes().
Raymond Hettinger <python@rcn.com>
parents: 29398
diff changeset
475 this method splits out smaller change clusters and eliminates
8c5a6853a02a Add docs for get_grouped_opcodes().
Raymond Hettinger <python@rcn.com>
parents: 29398
diff changeset
476 intervening ranges which have no changes.
8c5a6853a02a Add docs for get_grouped_opcodes().
Raymond Hettinger <python@rcn.com>
parents: 29398
diff changeset
477
8c5a6853a02a Add docs for get_grouped_opcodes().
Raymond Hettinger <python@rcn.com>
parents: 29398
diff changeset
478 The groups are returned in the same format as \method{get_opcodes()}.
33462
5876636ca8c6 HtmlDiff corrections from Dan Gass, + trimmed trailing whitespace.
Tim Peters <tim.peters@gmail.com>
parents: 33448
diff changeset
479 \versionadded{2.3}
29404
8c5a6853a02a Add docs for get_grouped_opcodes().
Raymond Hettinger <python@rcn.com>
parents: 29398
diff changeset
480 \end{methoddesc}
8c5a6853a02a Add docs for get_grouped_opcodes().
Raymond Hettinger <python@rcn.com>
parents: 29398
diff changeset
481
16682
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Fred Drake <fdrake@acm.org>
parents:
diff changeset
482 \begin{methoddesc}{ratio}{}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
483 Return a measure of the sequences' similarity as a float in the
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
484 range [0, 1].
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
485
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
486 Where T is the total number of elements in both sequences, and M is
19232
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
487 the number of matches, this is 2.0*M / T. Note that this is
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
488 \code{1.0} if the sequences are identical, and \code{0.0} if they
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
489 have nothing in common.
16682
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
490
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
491 This is expensive to compute if \method{get_matching_blocks()} or
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
492 \method{get_opcodes()} hasn't already been called, in which case you
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
493 may want to try \method{quick_ratio()} or
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
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494 \method{real_quick_ratio()} first to get an upper bound.
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
495 \end{methoddesc}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
496
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
497 \begin{methoddesc}{quick_ratio}{}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
498 Return an upper bound on \method{ratio()} relatively quickly.
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
499
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
500 This isn't defined beyond that it is an upper bound on
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
501 \method{ratio()}, and is faster to compute.
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
502 \end{methoddesc}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
503
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
504 \begin{methoddesc}{real_quick_ratio}{}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
505 Return an upper bound on \method{ratio()} very quickly.
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
506
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
507 This isn't defined beyond that it is an upper bound on
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
508 \method{ratio()}, and is faster to compute than either
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
509 \method{ratio()} or \method{quick_ratio()}.
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
510 \end{methoddesc}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
511
16703
8172906c6dc8 Improve accuracy. In the .tex file, note the new "% BUG:" comments: an
Tim Peters <tim.peters@gmail.com>
parents: 16682
diff changeset
512 The three methods that return the ratio of matching to total characters
8172906c6dc8 Improve accuracy. In the .tex file, note the new "% BUG:" comments: an
Tim Peters <tim.peters@gmail.com>
parents: 16682
diff changeset
513 can give different results due to differing levels of approximation,
8172906c6dc8 Improve accuracy. In the .tex file, note the new "% BUG:" comments: an
Tim Peters <tim.peters@gmail.com>
parents: 16682
diff changeset
514 although \method{quick_ratio()} and \method{real_quick_ratio()} are always
8172906c6dc8 Improve accuracy. In the .tex file, note the new "% BUG:" comments: an
Tim Peters <tim.peters@gmail.com>
parents: 16682
diff changeset
515 at least as large as \method{ratio()}:
16682
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
516
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
517 \begin{verbatim}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
518 >>> s = SequenceMatcher(None, "abcd", "bcde")
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
519 >>> s.ratio()
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
520 0.75
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
521 >>> s.quick_ratio()
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
522 0.75
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
523 >>> s.real_quick_ratio()
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
524 1.0
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
525 \end{verbatim}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
526
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
527
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Fred Drake <fdrake@acm.org>
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528 \subsection{SequenceMatcher Examples \label{sequencematcher-examples}}
16682
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
529
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
530
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
531 This example compares two strings, considering blanks to be ``junk:''
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
532
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
533 \begin{verbatim}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
534 >>> s = SequenceMatcher(lambda x: x == " ",
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
535 ... "private Thread currentThread;",
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
536 ... "private volatile Thread currentThread;")
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
537 \end{verbatim}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
538
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
539 \method{ratio()} returns a float in [0, 1], measuring the similarity
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
540 of the sequences. As a rule of thumb, a \method{ratio()} value over
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
541 0.6 means the sequences are close matches:
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
542
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
543 \begin{verbatim}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
544 >>> print round(s.ratio(), 3)
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
545 0.866
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
546 \end{verbatim}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
547
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
548 If you're only interested in where the sequences match,
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
549 \method{get_matching_blocks()} is handy:
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
550
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
551 \begin{verbatim}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
552 >>> for block in s.get_matching_blocks():
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
553 ... print "a[%d] and b[%d] match for %d elements" % block
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
554 a[0] and b[0] match for 8 elements
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
555 a[8] and b[17] match for 6 elements
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
556 a[14] and b[23] match for 15 elements
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
557 a[29] and b[38] match for 0 elements
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
558 \end{verbatim}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
559
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
560 Note that the last tuple returned by \method{get_matching_blocks()} is
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
561 always a dummy, \code{(len(\var{a}), len(\var{b}), 0)}, and this is
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
562 the only case in which the last tuple element (number of elements
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
563 matched) is \code{0}.
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
564
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
565 If you want to know how to change the first sequence into the second,
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
566 use \method{get_opcodes()}:
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
567
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
568 \begin{verbatim}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
569 >>> for opcode in s.get_opcodes():
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
570 ... print "%6s a[%d:%d] b[%d:%d]" % opcode
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
571 equal a[0:8] b[0:8]
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
572 insert a[8:8] b[8:17]
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
573 equal a[8:14] b[17:23]
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
574 equal a[14:29] b[23:38]
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
575 \end{verbatim}
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
576
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
577 See also the function \function{get_close_matches()} in this module,
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
578 which shows how simple code building on \class{SequenceMatcher} can be
3cb00cbe7455 Documentation for the difflib module, converted from the module docstrings.
Fred Drake <fdrake@acm.org>
parents:
diff changeset
579 used to do useful work.
19232
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diff changeset
580
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
581
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
582 \subsection{Differ Objects \label{differ-objects}}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
583
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
584 Note that \class{Differ}-generated deltas make no claim to be
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
585 \strong{minimal} diffs. To the contrary, minimal diffs are often
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
586 counter-intuitive, because they synch up anywhere possible, sometimes
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
587 accidental matches 100 pages apart. Restricting synch points to
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
588 contiguous matches preserves some notion of locality, at the
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
589 occasional cost of producing a longer diff.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
590
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
591 The \class{Differ} class has this constructor:
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
592
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
593 \begin{classdesc}{Differ}{\optional{linejunk\optional{, charjunk}}}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
594 Optional keyword parameters \var{linejunk} and \var{charjunk} are
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
595 for filter functions (or \code{None}):
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
596
23300
b5f6e9f6e7f4 Mostly in SequenceMatcher.{__chain_b, find_longest_match}:
Tim Peters <tim.peters@gmail.com>
parents: 21106
diff changeset
597 \var{linejunk}: A function that accepts a single string
b5f6e9f6e7f4 Mostly in SequenceMatcher.{__chain_b, find_longest_match}:
Tim Peters <tim.peters@gmail.com>
parents: 21106
diff changeset
598 argument, and returns true if the string is junk. The default is
b5f6e9f6e7f4 Mostly in SequenceMatcher.{__chain_b, find_longest_match}:
Tim Peters <tim.peters@gmail.com>
parents: 21106
diff changeset
599 \code{None}, meaning that no line is considered junk.
19232
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diff changeset
600
23300
b5f6e9f6e7f4 Mostly in SequenceMatcher.{__chain_b, find_longest_match}:
Tim Peters <tim.peters@gmail.com>
parents: 21106
diff changeset
601 \var{charjunk}: A function that accepts a single character argument
b5f6e9f6e7f4 Mostly in SequenceMatcher.{__chain_b, find_longest_match}:
Tim Peters <tim.peters@gmail.com>
parents: 21106
diff changeset
602 (a string of length 1), and returns true if the character is junk.
b5f6e9f6e7f4 Mostly in SequenceMatcher.{__chain_b, find_longest_match}:
Tim Peters <tim.peters@gmail.com>
parents: 21106
diff changeset
603 The default is \code{None}, meaning that no character is
b5f6e9f6e7f4 Mostly in SequenceMatcher.{__chain_b, find_longest_match}:
Tim Peters <tim.peters@gmail.com>
parents: 21106
diff changeset
604 considered junk.
19232
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diff changeset
605 \end{classdesc}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
606
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
607 \class{Differ} objects are used (deltas generated) via a single
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
608 method:
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
609
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
610 \begin{methoddesc}{compare}{a, b}
20038
8a6f2ee6eaba Make difflib.ndiff() and difflib.Differ.compare() generators. This
Tim Peters <tim.peters@gmail.com>
parents: 19232
diff changeset
611 Compare two sequences of lines, and generate the delta (a sequence
8a6f2ee6eaba Make difflib.ndiff() and difflib.Differ.compare() generators. This
Tim Peters <tim.peters@gmail.com>
parents: 19232
diff changeset
612 of lines).
19232
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
613
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
614 Each sequence must contain individual single-line strings ending
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
615 with newlines. Such sequences can be obtained from the
20038
8a6f2ee6eaba Make difflib.ndiff() and difflib.Differ.compare() generators. This
Tim Peters <tim.peters@gmail.com>
parents: 19232
diff changeset
616 \method{readlines()} method of file-like objects. The delta generated
8a6f2ee6eaba Make difflib.ndiff() and difflib.Differ.compare() generators. This
Tim Peters <tim.peters@gmail.com>
parents: 19232
diff changeset
617 also consists of newline-terminated strings, ready to be printed as-is
21106
3827f136e0d6 writeline() --> writelines()
Fred Drake <fdrake@acm.org>
parents: 20677
diff changeset
618 via the \method{writelines()} method of a file-like object.
19232
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
619 \end{methoddesc}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
620
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
621
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
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diff changeset
622 \subsection{Differ Example \label{differ-examples}}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
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parents: 17785
diff changeset
623
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
624 This example compares two texts. First we set up the texts, sequences
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
625 of individual single-line strings ending with newlines (such sequences
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
626 can also be obtained from the \method{readlines()} method of file-like
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
627 objects):
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
628
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
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diff changeset
629 \begin{verbatim}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
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diff changeset
630 >>> text1 = ''' 1. Beautiful is better than ugly.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
631 ... 2. Explicit is better than implicit.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
632 ... 3. Simple is better than complex.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
633 ... 4. Complex is better than complicated.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
634 ... '''.splitlines(1)
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
635 >>> len(text1)
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
636 4
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
637 >>> text1[0][-1]
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
638 '\n'
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
639 >>> text2 = ''' 1. Beautiful is better than ugly.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
640 ... 3. Simple is better than complex.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
641 ... 4. Complicated is better than complex.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
642 ... 5. Flat is better than nested.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
643 ... '''.splitlines(1)
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
644 \end{verbatim}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
645
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
646 Next we instantiate a Differ object:
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
647
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
648 \begin{verbatim}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
649 >>> d = Differ()
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
650 \end{verbatim}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
651
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
652 Note that when instantiating a \class{Differ} object we may pass
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
653 functions to filter out line and character ``junk.'' See the
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
654 \method{Differ()} constructor for details.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
655
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
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parents: 17785
diff changeset
656 Finally, we compare the two:
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
657
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
658 \begin{verbatim}
20038
8a6f2ee6eaba Make difflib.ndiff() and difflib.Differ.compare() generators. This
Tim Peters <tim.peters@gmail.com>
parents: 19232
diff changeset
659 >>> result = list(d.compare(text1, text2))
19232
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
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diff changeset
660 \end{verbatim}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
661
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
662 \code{result} is a list of strings, so let's pretty-print it:
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
663
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
664 \begin{verbatim}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
665 >>> from pprint import pprint
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
666 >>> pprint(result)
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
667 [' 1. Beautiful is better than ugly.\n',
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
668 '- 2. Explicit is better than implicit.\n',
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
669 '- 3. Simple is better than complex.\n',
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
670 '+ 3. Simple is better than complex.\n',
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
671 '? ++ \n',
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
672 '- 4. Complex is better than complicated.\n',
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
673 '? ^ ---- ^ \n',
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
674 '+ 4. Complicated is better than complex.\n',
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
675 '? ++++ ^ ^ \n',
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
676 '+ 5. Flat is better than nested.\n']
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
677 \end{verbatim}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
678
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
679 As a single multi-line string it looks like this:
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
680
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
681 \begin{verbatim}
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
682 >>> import sys
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
683 >>> sys.stdout.writelines(result)
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
684 1. Beautiful is better than ugly.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
685 - 2. Explicit is better than implicit.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
686 - 3. Simple is better than complex.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
687 + 3. Simple is better than complex.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
688 ? ++
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
689 - 4. Complex is better than complicated.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
690 ? ^ ---- ^
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
691 + 4. Complicated is better than complex.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
692 ? ++++ ^ ^
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
693 + 5. Flat is better than nested.
65885ea76c37 David Goodger <dgoodger@atsautomation.com>:
Fred Drake <fdrake@acm.org>
parents: 17785
diff changeset
694 \end{verbatim}