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74eda76085
Perhaps the BytesParser 'text' argument should really be bytes, but it hasn't been, it has been text, so for backward compatibility and for consistency with the regular Parser class, I'm keeping it as 'text'.
312 lines
14 KiB
ReStructuredText
312 lines
14 KiB
ReStructuredText
:mod:`email.parser`: Parsing email messages
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-------------------------------------------
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.. module:: email.parser
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:synopsis: Parse flat text email messages to produce a message object structure.
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**Source code:** :source:`Lib/email/parser.py`
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--------------
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Message object structures can be created in one of two ways: they can be created
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from whole cloth by instantiating :class:`~email.message.Message` objects and
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stringing them together via :meth:`~email.message.Message.attach` and
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:meth:`~email.message.Message.set_payload` calls, or they
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can be created by parsing a flat text representation of the email message.
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The :mod:`email` package provides a standard parser that understands most email
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document structures, including MIME documents. You can pass the parser a string
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or a file object, and the parser will return to you the root
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:class:`~email.message.Message` instance of the object structure. For simple,
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non-MIME messages the payload of this root object will likely be a string
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containing the text of the message. For MIME messages, the root object will
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return ``True`` from its :meth:`~email.message.Message.is_multipart` method, and
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the subparts can be accessed via the :meth:`~email.message.Message.get_payload`
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and :meth:`~email.message.Message.walk` methods.
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There are actually two parser interfaces available for use, the classic
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:class:`Parser` API and the incremental :class:`FeedParser` API. The classic
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:class:`Parser` API is fine if you have the entire text of the message in memory
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as a string, or if the entire message lives in a file on the file system.
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:class:`FeedParser` is more appropriate for when you're reading the message from
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a stream which might block waiting for more input (e.g. reading an email message
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from a socket). The :class:`FeedParser` can consume and parse the message
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incrementally, and only returns the root object when you close the parser [#]_.
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Note that the parser can be extended in limited ways, and of course you can
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implement your own parser completely from scratch. There is no magical
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connection between the :mod:`email` package's bundled parser and the
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:class:`~email.message.Message` class, so your custom parser can create message
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object trees any way it finds necessary.
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FeedParser API
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^^^^^^^^^^^^^^
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The :class:`FeedParser`, imported from the :mod:`email.feedparser` module,
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provides an API that is conducive to incremental parsing of email messages, such
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as would be necessary when reading the text of an email message from a source
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that can block (e.g. a socket). The :class:`FeedParser` can of course be used
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to parse an email message fully contained in a string or a file, but the classic
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:class:`Parser` API may be more convenient for such use cases. The semantics
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and results of the two parser APIs are identical.
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The :class:`FeedParser`'s API is simple; you create an instance, feed it a bunch
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of text until there's no more to feed it, then close the parser to retrieve the
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root message object. The :class:`FeedParser` is extremely accurate when parsing
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standards-compliant messages, and it does a very good job of parsing
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non-compliant messages, providing information about how a message was deemed
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broken. It will populate a message object's *defects* attribute with a list of
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any problems it found in a message. See the :mod:`email.errors` module for the
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list of defects that it can find.
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Here is the API for the :class:`FeedParser`:
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.. class:: FeedParser(_factory=email.message.Message, *, policy=policy.compat32)
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Create a :class:`FeedParser` instance. Optional *_factory* is a no-argument
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callable that will be called whenever a new message object is needed. It
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defaults to the :class:`email.message.Message` class.
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If *policy* is specified (it must be an instance of a :mod:`~email.policy`
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class) use the rules it specifies to update the representation of the
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message. If *policy* is not set, use the :class:`compat32
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<email.policy.Compat32>` policy, which maintains backward compatibility with
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the Python 3.2 version of the email package. For more information see the
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:mod:`~email.policy` documentation.
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.. versionchanged:: 3.3 Added the *policy* keyword.
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.. method:: feed(data)
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Feed the :class:`FeedParser` some more data. *data* should be a string
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containing one or more lines. The lines can be partial and the
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:class:`FeedParser` will stitch such partial lines together properly. The
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lines in the string can have any of the common three line endings,
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carriage return, newline, or carriage return and newline (they can even be
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mixed).
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.. method:: close()
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Closing a :class:`FeedParser` completes the parsing of all previously fed
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data, and returns the root message object. It is undefined what happens
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if you feed more data to a closed :class:`FeedParser`.
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.. class:: BytesFeedParser(_factory=email.message.Message)
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Works exactly like :class:`FeedParser` except that the input to the
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:meth:`~FeedParser.feed` method must be bytes and not string.
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.. versionadded:: 3.2
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Parser class API
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^^^^^^^^^^^^^^^^
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The :class:`Parser` class, imported from the :mod:`email.parser` module,
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provides an API that can be used to parse a message when the complete contents
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of the message are available in a string or file. The :mod:`email.parser`
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module also provides header-only parsers, called :class:`HeaderParser` and
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:class:`BytesHeaderParser`, which can be used if you're only interested in the
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headers of the message. :class:`HeaderParser` and :class:`BytesHeaderParser`
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can be much faster in these situations, since they do not attempt to parse the
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message body, instead setting the payload to the raw body as a string. They
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have the same API as the :class:`Parser` and :class:`BytesParser` classes.
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.. versionadded:: 3.3
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The BytesHeaderParser class.
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.. class:: Parser(_class=email.message.Message, *, policy=policy.compat32)
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The constructor for the :class:`Parser` class takes an optional argument
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*_class*. This must be a callable factory (such as a function or a class), and
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it is used whenever a sub-message object needs to be created. It defaults to
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:class:`~email.message.Message` (see :mod:`email.message`). The factory will
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be called without arguments.
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If *policy* is specified (it must be an instance of a :mod:`~email.policy`
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class) use the rules it specifies to update the representation of the
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message. If *policy* is not set, use the :class:`compat32
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<email.policy.Compat32>` policy, which maintains backward compatibility with
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the Python 3.2 version of the email package. For more information see the
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:mod:`~email.policy` documentation.
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.. versionchanged:: 3.3
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Removed the *strict* argument that was deprecated in 2.4. Added the
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*policy* keyword.
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The other public :class:`Parser` methods are:
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.. method:: parse(fp, headersonly=False)
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Read all the data from the file-like object *fp*, parse the resulting
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text, and return the root message object. *fp* must support both the
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:meth:`~io.TextIOBase.readline` and the :meth:`~io.TextIOBase.read`
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methods on file-like objects.
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The text contained in *fp* must be formatted as a block of :rfc:`2822`
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style headers and header continuation lines, optionally preceded by an
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envelope header. The header block is terminated either by the end of the
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data or by a blank line. Following the header block is the body of the
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message (which may contain MIME-encoded subparts).
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Optional *headersonly* is a flag specifying whether to stop parsing after
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reading the headers or not. The default is ``False``, meaning it parses
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the entire contents of the file.
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.. method:: parsestr(text, headersonly=False)
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Similar to the :meth:`parse` method, except it takes a string object
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instead of a file-like object. Calling this method on a string is exactly
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equivalent to wrapping *text* in a :class:`~io.StringIO` instance first and
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calling :meth:`parse`.
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Optional *headersonly* is as with the :meth:`parse` method.
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.. class:: BytesParser(_class=email.message.Message, *, policy=policy.compat32)
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This class is exactly parallel to :class:`Parser`, but handles bytes input.
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The *_class* and *strict* arguments are interpreted in the same way as for
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the :class:`Parser` constructor.
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If *policy* is specified (it must be an instance of a :mod:`~email.policy`
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class) use the rules it specifies to update the representation of the
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message. If *policy* is not set, use the :class:`compat32
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<email.policy.Compat32>` policy, which maintains backward compatibility with
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the Python 3.2 version of the email package. For more information see the
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:mod:`~email.policy` documentation.
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.. versionchanged:: 3.3
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Removed the *strict* argument. Added the *policy* keyword.
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.. method:: parse(fp, headersonly=False)
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Read all the data from the binary file-like object *fp*, parse the
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resulting bytes, and return the message object. *fp* must support
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both the :meth:`~io.IOBase.readline` and the :meth:`~io.IOBase.read`
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methods on file-like objects.
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The bytes contained in *fp* must be formatted as a block of :rfc:`2822`
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style headers and header continuation lines, optionally preceded by an
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envelope header. The header block is terminated either by the end of the
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data or by a blank line. Following the header block is the body of the
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message (which may contain MIME-encoded subparts, including subparts
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with a :mailheader:`Content-Transfer-Encoding` of ``8bit``.
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Optional *headersonly* is a flag specifying whether to stop parsing after
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reading the headers or not. The default is ``False``, meaning it parses
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the entire contents of the file.
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.. method:: parsebytes(text, headersonly=False)
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Similar to the :meth:`parse` method, except it takes a :term:`bytes-like
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object` instead of a file-like object. Calling this method is equivalent
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to wrapping *text* in a :class:`~io.BytesIO` instance first and calling
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:meth:`parse`.
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Optional *headersonly* is as with the :meth:`parse` method.
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.. versionadded:: 3.2
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Since creating a message object structure from a string or a file object is such
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a common task, four functions are provided as a convenience. They are available
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in the top-level :mod:`email` package namespace.
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.. currentmodule:: email
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.. function:: message_from_string(s, _class=email.message.Message, *, \
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policy=policy.compat32)
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Return a message object structure from a string. This is exactly equivalent to
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``Parser().parsestr(s)``. *_class* and *policy* are interpreted as
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with the :class:`~email.parser.Parser` class constructor.
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.. versionchanged:: 3.3
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Removed the *strict* argument. Added the *policy* keyword.
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.. function:: message_from_bytes(s, _class=email.message.Message, *, \
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policy=policy.compat32)
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Return a message object structure from a :term:`bytes-like object`. This is exactly
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equivalent to ``BytesParser().parsebytes(s)``. Optional *_class* and
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*strict* are interpreted as with the :class:`~email.parser.Parser` class
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constructor.
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.. versionadded:: 3.2
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.. versionchanged:: 3.3
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Removed the *strict* argument. Added the *policy* keyword.
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.. function:: message_from_file(fp, _class=email.message.Message, *, \
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policy=policy.compat32)
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Return a message object structure tree from an open :term:`file object`.
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This is exactly equivalent to ``Parser().parse(fp)``. *_class*
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and *policy* are interpreted as with the :class:`~email.parser.Parser` class
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constructor.
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.. versionchanged:: 3.3
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Removed the *strict* argument. Added the *policy* keyword.
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.. function:: message_from_binary_file(fp, _class=email.message.Message, *, \
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policy=policy.compat32)
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Return a message object structure tree from an open binary :term:`file
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object`. This is exactly equivalent to ``BytesParser().parse(fp)``.
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*_class* and *policy* are interpreted as with the
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:class:`~email.parser.Parser` class constructor.
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.. versionadded:: 3.2
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.. versionchanged:: 3.3
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Removed the *strict* argument. Added the *policy* keyword.
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Here's an example of how you might use this at an interactive Python prompt::
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>>> import email
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>>> msg = email.message_from_string(myString) # doctest: +SKIP
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Additional notes
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^^^^^^^^^^^^^^^^
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Here are some notes on the parsing semantics:
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* Most non-\ :mimetype:`multipart` type messages are parsed as a single message
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object with a string payload. These objects will return ``False`` for
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:meth:`~email.message.Message.is_multipart`. Their
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:meth:`~email.message.Message.get_payload` method will return a string object.
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* All :mimetype:`multipart` type messages will be parsed as a container message
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object with a list of sub-message objects for their payload. The outer
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container message will return ``True`` for
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:meth:`~email.message.Message.is_multipart` and their
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:meth:`~email.message.Message.get_payload` method will return the list of
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:class:`~email.message.Message` subparts.
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* Most messages with a content type of :mimetype:`message/\*` (e.g.
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:mimetype:`message/delivery-status` and :mimetype:`message/rfc822`) will also be
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parsed as container object containing a list payload of length 1. Their
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:meth:`~email.message.Message.is_multipart` method will return ``True``.
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The single element in the list payload will be a sub-message object.
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* Some non-standards compliant messages may not be internally consistent about
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their :mimetype:`multipart`\ -edness. Such messages may have a
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:mailheader:`Content-Type` header of type :mimetype:`multipart`, but their
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:meth:`~email.message.Message.is_multipart` method may return ``False``.
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If such messages were parsed with the :class:`~email.parser.FeedParser`,
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they will have an instance of the
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:class:`~email.errors.MultipartInvariantViolationDefect` class in their
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*defects* attribute list. See :mod:`email.errors` for details.
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.. rubric:: Footnotes
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.. [#] As of email package version 3.0, introduced in Python 2.4, the classic
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:class:`~email.parser.Parser` was re-implemented in terms of the
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:class:`~email.parser.FeedParser`, so the semantics and results are
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identical between the two parsers.
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