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restructure a bit to not rely on test case execution ordering add test case for bug #482460
author Skip Montanaro <skip@pobox.com>
date Sun, 17 Mar 2002 23:03:42 +0000
parents 52aa3e3e577f
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1 \declaremodule{standard}{email.Parser}
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2 \modulesynopsis{Parse flat text email messages to produce a message
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3 object tree.}
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4
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5 Message object trees can be created in one of two ways: they can be
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6 created from whole cloth by instantiating \class{Message} objects and
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7 stringing them together via \method{add_payload()} and
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8 \method{set_payload()} calls, or they can be created by parsing a flat text
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9 representation of the email message.
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10
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11 The \module{email} package provides a standard parser that understands
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12 most email document structures, including MIME documents. You can
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13 pass the parser a string or a file object, and the parser will return
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14 to you the root \class{Message} instance of the object tree. For
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15 simple, non-MIME messages the payload of this root object will likely
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16 be a string containing the text of the message. For MIME
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17 messages, the root object will return true from its
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18 \method{is_multipart()} method, and the subparts can be accessed via
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19 the \method{get_payload()} and \method{walk()} methods.
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20
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21 Note that the parser can be extended in limited ways, and of course
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22 you can implement your own parser completely from scratch. There is
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23 no magical connection between the \module{email} package's bundled
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24 parser and the \class{Message} class, so your custom parser can create
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25 message object trees any way it finds necessary.
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26
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27 The primary parser class is \class{Parser} which parses both the
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28 headers and the payload of the message. In the case of
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29 \mimetype{multipart} messages, it will recursively parse the body of
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30 the container message. The \module{email.Parser} module also provides
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31 a second class, called \class{HeaderParser} which can be used if
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32 you're only interested in the headers of the message.
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33 \class{HeaderParser} can be much faster in this situations, since it
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34 does not attempt to parse the message body, instead setting the
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35 payload to the raw body as a string. \class{HeaderParser} has the
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36 same API as the \class{Parser} class.
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37
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38 \subsubsection{Parser class API}
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39
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40 \begin{classdesc}{Parser}{\optional{_class}}
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41 The constructor for the \class{Parser} class takes a single optional
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42 argument \var{_class}. This must be a callable factory (such as a
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43 function or a class), and it is used whenever a sub-message object
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44 needs to be created. It defaults to \class{Message} (see
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45 \refmodule{email.Message}). The factory will be called without
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46 arguments.
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47 \end{classdesc}
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48
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49 The other public \class{Parser} methods are:
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50
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51 \begin{methoddesc}[Parser]{parse}{fp}
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52 Read all the data from the file-like object \var{fp}, parse the
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53 resulting text, and return the root message object. \var{fp} must
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54 support both the \method{readline()} and the \method{read()} methods
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55 on file-like objects.
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56
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57 The text contained in \var{fp} must be formatted as a block of \rfc{2822}
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58 style headers and header continuation lines, optionally preceeded by a
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59 \emph{Unix-From} header. The header block is terminated either by the
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60 end of the data or by a blank line. Following the header block is the
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61 body of the message (which may contain MIME-encoded subparts).
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62 \end{methoddesc}
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63
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64 \begin{methoddesc}[Parser]{parsestr}{text}
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65 Similar to the \method{parse()} method, except it takes a string
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66 object instead of a file-like object. Calling this method on a string
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67 is exactly equivalent to wrapping \var{text} in a \class{StringIO}
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68 instance first and calling \method{parse()}.
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69 \end{methoddesc}
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70
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71 Since creating a message object tree from a string or a file object is
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72 such a common task, two functions are provided as a convenience. They
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73 are available in the top-level \module{email} package namespace.
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74
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75 \begin{funcdesc}{message_from_string}{s\optional{, _class}}
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76 Return a message object tree from a string. This is exactly
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77 equivalent to \code{Parser().parsestr(s)}. Optional \var{_class} is
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78 interpreted as with the \class{Parser} class constructor.
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79 \end{funcdesc}
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80
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81 \begin{funcdesc}{message_from_file}{fp\optional{, _class}}
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82 Return a message object tree from an open file object. This is exactly
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83 equivalent to \code{Parser().parse(fp)}. Optional \var{_class} is
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84 interpreted as with the \class{Parser} class constructor.
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85 \end{funcdesc}
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86
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87 Here's an example of how you might use this at an interactive Python
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88 prompt:
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89
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90 \begin{verbatim}
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91 >>> import email
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92 >>> msg = email.message_from_string(myString)
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93 \end{verbatim}
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94
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95 \subsubsection{Additional notes}
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96
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97 Here are some notes on the parsing semantics:
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98
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99 \begin{itemize}
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100 \item Most non-\mimetype{multipart} type messages are parsed as a single
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101 message object with a string payload. These objects will return
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102 0 for \method{is_multipart()}.
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103 \item One exception is for \mimetype{message/delivery-status} type
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104 messages. Because the body of such messages consist of
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105 blocks of headers, \class{Parser} will create a non-multipart
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106 object containing non-multipart subobjects for each header
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107 block.
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108 \item Another exception is for \mimetype{message/*} types (more
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109 general than \mimetype{message/delivery-status}). These are
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110 typically \mimetype{message/rfc822} messages, represented as a
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111 non-multipart object containing a singleton payload which is
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112 another non-multipart \class{Message} instance.
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113 \end{itemize}