1 :mod:`email`: Parsing email messages
2 ------------------------------------
4 .. module:: email.parser
5 :synopsis: Parse flat text email messages to produce a message object structure.
8 Message object structures can be created in one of two ways: they can be created
9 from whole cloth by instantiating :class:`Message` objects and stringing them
10 together via :meth:`attach` and :meth:`set_payload` calls, or they can be
11 created by parsing a flat text representation of the email message.
13 The :mod:`email` package provides a standard parser that understands most email
14 document structures, including MIME documents. You can pass the parser a string
15 or a file object, and the parser will return to you the root :class:`Message`
16 instance of the object structure. For simple, non-MIME messages the payload of
17 this root object will likely be a string containing the text of the message.
18 For MIME messages, the root object will return ``True`` from its
19 :meth:`is_multipart` method, and the subparts can be accessed via the
20 :meth:`get_payload` and :meth:`walk` methods.
22 There are actually two parser interfaces available for use, the classic
23 :class:`Parser` API and the incremental :class:`FeedParser` API. The classic
24 :class:`Parser` API is fine if you have the entire text of the message in memory
25 as a string, or if the entire message lives in a file on the file system.
26 :class:`FeedParser` is more appropriate for when you're reading the message from
27 a stream which might block waiting for more input (e.g. reading an email message
28 from a socket). The :class:`FeedParser` can consume and parse the message
29 incrementally, and only returns the root object when you close the parser [#]_.
31 Note that the parser can be extended in limited ways, and of course you can
32 implement your own parser completely from scratch. There is no magical
33 connection between the :mod:`email` package's bundled parser and the
34 :class:`Message` class, so your custom parser can create message object trees
35 any way it finds necessary.
43 The :class:`FeedParser`, imported from the :mod:`email.feedparser` module,
44 provides an API that is conducive to incremental parsing of email messages, such
45 as would be necessary when reading the text of an email message from a source
46 that can block (e.g. a socket). The :class:`FeedParser` can of course be used
47 to parse an email message fully contained in a string or a file, but the classic
48 :class:`Parser` API may be more convenient for such use cases. The semantics
49 and results of the two parser APIs are identical.
51 The :class:`FeedParser`'s API is simple; you create an instance, feed it a bunch
52 of text until there's no more to feed it, then close the parser to retrieve the
53 root message object. The :class:`FeedParser` is extremely accurate when parsing
54 standards-compliant messages, and it does a very good job of parsing
55 non-compliant messages, providing information about how a message was deemed
56 broken. It will populate a message object's *defects* attribute with a list of
57 any problems it found in a message. See the :mod:`email.errors` module for the
58 list of defects that it can find.
60 Here is the API for the :class:`FeedParser`:
63 .. class:: FeedParser([_factory])
65 Create a :class:`FeedParser` instance. Optional *_factory* is a no-argument
66 callable that will be called whenever a new message object is needed. It
67 defaults to the :class:`email.message.Message` class.
70 .. method:: FeedParser.feed(data)
72 Feed the :class:`FeedParser` some more data. *data* should be a string
73 containing one or more lines. The lines can be partial and the
74 :class:`FeedParser` will stitch such partial lines together properly. The lines
75 in the string can have any of the common three line endings, carriage return,
76 newline, or carriage return and newline (they can even be mixed).
79 .. method:: FeedParser.close()
81 Closing a :class:`FeedParser` completes the parsing of all previously fed data,
82 and returns the root message object. It is undefined what happens if you feed
83 more data to a closed :class:`FeedParser`.
89 The :class:`Parser` class, imported from the :mod:`email.parser` module,
90 provides an API that can be used to parse a message when the complete contents
91 of the message are available in a string or file. The :mod:`email.parser`
92 module also provides a second class, called :class:`HeaderParser` which can be
93 used if you're only interested in the headers of the message.
94 :class:`HeaderParser` can be much faster in these situations, since it does not
95 attempt to parse the message body, instead setting the payload to the raw body
96 as a string. :class:`HeaderParser` has the same API as the :class:`Parser`
100 .. class:: Parser([_class])
102 The constructor for the :class:`Parser` class takes an optional argument
103 *_class*. This must be a callable factory (such as a function or a class), and
104 it is used whenever a sub-message object needs to be created. It defaults to
105 :class:`Message` (see :mod:`email.message`). The factory will be called without
108 The optional *strict* flag is ignored.
111 Because the :class:`Parser` class is a backward compatible API wrapper
112 around the new-in-Python 2.4 :class:`FeedParser`, *all* parsing is
113 effectively non-strict. You should simply stop passing a *strict* flag to
114 the :class:`Parser` constructor.
116 .. versionchanged:: 2.2.2
117 The *strict* flag was added.
119 .. versionchanged:: 2.4
120 The *strict* flag was deprecated.
122 The other public :class:`Parser` methods are:
125 .. method:: Parser.parse(fp[, headersonly])
127 Read all the data from the file-like object *fp*, parse the resulting text, and
128 return the root message object. *fp* must support both the :meth:`readline` and
129 the :meth:`read` methods on file-like objects.
131 The text contained in *fp* must be formatted as a block of :rfc:`2822` style
132 headers and header continuation lines, optionally preceded by a envelope
133 header. The header block is terminated either by the end of the data or by a
134 blank line. Following the header block is the body of the message (which may
135 contain MIME-encoded subparts).
137 Optional *headersonly* is as with the :meth:`parse` method.
139 .. versionchanged:: 2.2.2
140 The *headersonly* flag was added.
143 .. method:: Parser.parsestr(text[, headersonly])
145 Similar to the :meth:`parse` method, except it takes a string object instead of
146 a file-like object. Calling this method on a string is exactly equivalent to
147 wrapping *text* in a :class:`StringIO` instance first and calling :meth:`parse`.
149 Optional *headersonly* is a flag specifying whether to stop parsing after
150 reading the headers or not. The default is ``False``, meaning it parses the
151 entire contents of the file.
153 .. versionchanged:: 2.2.2
154 The *headersonly* flag was added.
156 Since creating a message object structure from a string or a file object is such
157 a common task, two functions are provided as a convenience. They are available
158 in the top-level :mod:`email` package namespace.
161 .. function:: message_from_string(s[, _class[, strict]])
163 Return a message object structure from a string. This is exactly equivalent to
164 ``Parser().parsestr(s)``. Optional *_class* and *strict* are interpreted as
165 with the :class:`Parser` class constructor.
167 .. versionchanged:: 2.2.2
168 The *strict* flag was added.
171 .. function:: message_from_file(fp[, _class[, strict]])
173 Return a message object structure tree from an open file object. This is
174 exactly equivalent to ``Parser().parse(fp)``. Optional *_class* and *strict*
175 are interpreted as with the :class:`Parser` class constructor.
177 .. versionchanged:: 2.2.2
178 The *strict* flag was added.
180 Here's an example of how you might use this at an interactive Python prompt::
183 >>> msg = email.message_from_string(myString)
189 Here are some notes on the parsing semantics:
191 * Most non-\ :mimetype:`multipart` type messages are parsed as a single message
192 object with a string payload. These objects will return ``False`` for
193 :meth:`is_multipart`. Their :meth:`get_payload` method will return a string
196 * All :mimetype:`multipart` type messages will be parsed as a container message
197 object with a list of sub-message objects for their payload. The outer
198 container message will return ``True`` for :meth:`is_multipart` and their
199 :meth:`get_payload` method will return the list of :class:`Message` subparts.
201 * Most messages with a content type of :mimetype:`message/\*` (e.g.
202 :mimetype:`message/delivery-status` and :mimetype:`message/rfc822`) will also be
203 parsed as container object containing a list payload of length 1. Their
204 :meth:`is_multipart` method will return ``True``. The single element in the
205 list payload will be a sub-message object.
207 * Some non-standards compliant messages may not be internally consistent about
208 their :mimetype:`multipart`\ -edness. Such messages may have a
209 :mailheader:`Content-Type` header of type :mimetype:`multipart`, but their
210 :meth:`is_multipart` method may return ``False``. If such messages were parsed
211 with the :class:`FeedParser`, they will have an instance of the
212 :class:`MultipartInvariantViolationDefect` class in their *defects* attribute
213 list. See :mod:`email.errors` for details.
215 .. rubric:: Footnotes
217 .. [#] As of email package version 3.0, introduced in Python 2.4, the classic
218 :class:`Parser` was re-implemented in terms of the :class:`FeedParser`, so the
219 semantics and results are identical between the two parsers.