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321 lines
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ReStructuredText
321 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
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created from whole cloth by creating an :class:`~email.message.EmailMessage`
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object, adding headers using the dictionary interface, and adding payload(s)
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using :meth:`~email.message.EmailMessage.set_content` and related methods, or
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they can be created by parsing a serialized representation of the email
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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
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bytes, string or file object, and the parser will return to you the root
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:class:`~email.message.EmailMessage` instance of the object structure. For
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simple, non-MIME messages the payload of this root object will likely be a
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string containing the text of the message. For MIME messages, the root object
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will return ``True`` from its :meth:`~email.message.EmailMessage.is_multipart`
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method, and the subparts can be accessed via the payload manipulation methods,
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such as :meth:`~email.message.EmailMessage.get_body`,
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:meth:`~email.message.EmailMessage.iter_parts`, and
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:meth:`~email.message.EmailMessage.walk`.
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There are actually two parser interfaces available for use, the :class:`Parser`
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API and the incremental :class:`FeedParser` API. The :class:`Parser` API is
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most useful if you have the entire text of the message in memory, or if the
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entire message lives in a file on the file system. :class:`FeedParser` is more
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appropriate when you are reading the message from a stream which might block
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waiting for more input (such as reading an email message from a socket). The
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:class:`FeedParser` can consume and parse the message incrementally, and only
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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. All of the logic that
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connects the :mod:`email` package's bundled parser and the
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:class:`~email.message.EmailMessage` class is embodied in the :mod:`policy`
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class, so a custom parser can create message object trees any way it finds
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necessary by implementing custom versions of the appropriate :mod:`policy`
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methods.
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FeedParser API
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^^^^^^^^^^^^^^
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The :class:`BytesFeedParser`, imported from the :mod:`email.feedparser` module,
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provides an API that is conducive to incremental parsing of email messages,
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such as would be necessary when reading the text of an email message from a
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source that can block (such as a socket). The :class:`BytesFeedParser` can of
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course be used to parse an email message fully contained in a :term:`bytes-like
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object`, string, or file, but the :class:`BytesParser` API may be more
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convenient for such use cases. The semantics and results of the two parser
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APIs are identical.
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The :class:`BytesFeedParser`'s API is simple; you create an instance, feed it a
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bunch of bytes until there's no more to feed it, then close the parser to
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retrieve the root message object. The :class:`BytesFeedParser` is extremely
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accurate when parsing standards-compliant messages, and it does a very good job
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of parsing non-compliant messages, providing information about how a message
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was deemed broken. It will populate a message object's
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:attr:`~email.message.EmailMessage.defects` attribute with a list of any
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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:`BytesFeedParser`:
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.. class:: BytesFeedParser(_factory=None, *, policy=policy.compat32)
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Create a :class:`BytesFeedParser` instance. Optional *_factory* is a
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no-argument callable; if not specified use the
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:attr:`~email.policy.Policy.message_factory` from the *policy*. Call
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*_factory* whenever a new message object is needed.
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If *policy* is specified use the rules it specifies to update the
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representation of the message. If *policy* is not set, use the
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:class:`compat32 <email.policy.Compat32>` policy, which maintains backward
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compatibility with the Python 3.2 version of the email package and provides
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:class:`~email.message.Message` as the default factory. All other policies
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provide :class:`~email.message.EmailMessage` as the default *_factory*. For
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more information on what else *policy* controls, see the
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:mod:`~email.policy` documentation.
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Note: **The policy keyword should always be specified**; The default will
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change to :data:`email.policy.default` in a future version of Python.
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.. versionadded:: 3.2
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.. versionchanged:: 3.3 Added the *policy* keyword.
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.. versionchanged:: 3.6 *_factory* defaults to the policy ``message_factory``.
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.. method:: feed(data)
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Feed the parser some more data. *data* should be a :term:`bytes-like
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object` containing one or more lines. The lines can be partial and the
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parser will stitch such partial lines together properly. The lines can
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have any of the three common line endings: carriage return, newline, or
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carriage return and newline (they can even be mixed).
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.. method:: close()
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Complete the parsing of all previously fed data and return the root
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message object. It is undefined what happens if :meth:`~feed` is called
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after this method has been called.
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.. class:: FeedParser(_factory=None, *, policy=policy.compat32)
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Works like :class:`BytesFeedParser` except that the input to the
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:meth:`~BytesFeedParser.feed` method must be a string. This is of limited
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utility, since the only way for such a message to be valid is for it to
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contain only ASCII text or, if :attr:`~email.policy.Policy.utf8` is
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``True``, no binary attachments.
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.. versionchanged:: 3.3 Added the *policy* keyword.
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Parser API
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^^^^^^^^^^
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The :class:`BytesParser` 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 :term:`bytes-like object` or file. The
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:mod:`email.parser` module also provides :class:`Parser` for parsing strings,
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and header-only parsers, :class:`BytesHeaderParser` and
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:class:`HeaderParser`, which can be used if you're only interested in the
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headers of the message. :class:`BytesHeaderParser` and :class:`HeaderParser`
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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.
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.. class:: BytesParser(_class=None, *, policy=policy.compat32)
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Create a :class:`BytesParser` instance. The *_class* and *policy*
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arguments have the same meaning and sematnics as the *_factory*
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and *policy* arguments of :class:`BytesFeedParser`.
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Note: **The policy keyword should always be specified**; The default will
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change to :data:`email.policy.default` in a future version of Python.
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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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.. versionchanged:: 3.6 *_class* defaults to the policy ``message_factory``.
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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.
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The bytes contained in *fp* must be formatted as a block of :rfc:`5322`
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(or, if :attr:`~email.policy.Policy.utf8` is ``True``, :rfc:`6532`)
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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(bytes, 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 on a
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:term:`bytes-like object` is equivalent to wrapping *bytes* in a
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:class:`~io.BytesIO` instance first and calling :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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.. class:: BytesHeaderParser(_class=None, *, policy=policy.compat32)
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Exactly like :class:`BytesParser`, except that *headersonly*
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defaults to ``True``.
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.. versionadded:: 3.3
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.. class:: Parser(_class=None, *, policy=policy.compat32)
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This class is parallel to :class:`BytesParser`, but handles string input.
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.. versionchanged:: 3.3
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Removed the *strict* argument. Added the *policy* keyword.
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.. versionchanged:: 3.6 *_class* defaults to the policy ``message_factory``.
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.. method:: parse(fp, headersonly=False)
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Read all the data from the text-mode file-like object *fp*, parse the
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resulting text, and return the root message object. *fp* must support
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both the :meth:`~io.TextIOBase.readline` and the
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:meth:`~io.TextIOBase.read` methods on file-like objects.
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Other than the text mode requirement, this method operates like
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:meth:`BytesParser.parse`.
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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
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equivalent to wrapping *text* in a :class:`~io.StringIO` instance first
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and calling :meth:`parse`.
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Optional *headersonly* is as with the :meth:`parse` method.
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.. class:: HeaderParser(_class=None, *, policy=policy.compat32)
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Exactly like :class:`Parser`, except that *headersonly*
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defaults to ``True``.
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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_bytes(s, _class=None, *, policy=policy.compat32)
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Return a message object structure from a :term:`bytes-like object`. This is
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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.BytesParser` 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_binary_file(fp, _class=None, *,
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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 equivalent to ``BytesParser().parse(fp)``. *_class* and
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*policy* are interpreted as with the :class:`~email.parser.BytesParser` 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_string(s, _class=None, *, policy=policy.compat32)
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Return a message object structure from a string. This is 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_file(fp, _class=None, *, 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 equivalent to ``Parser().parse(fp)``. *_class* and *policy* are
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interpreted as 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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.. versionchanged:: 3.6 *_class* defaults to the policy ``message_factory``.
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Here's an example of how you might use :func:`message_from_bytes` at an
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interactive Python prompt::
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>>> import email
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>>> msg = email.message_from_bytes(myBytes) # 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.EmailMessage.is_multipart`, and
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:meth:`~email.message.EmailMessage.iter_parts` will yield an empty list.
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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.EmailMessage.is_multipart`, and
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:meth:`~email.message.EmailMessage.iter_parts` will yield a list of subparts.
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* Most messages with a content type of :mimetype:`message/\*` (such as
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:mimetype:`message/delivery-status` and :mimetype:`message/rfc822`) will also
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be parsed as container object containing a list payload of length 1. Their
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:meth:`~email.message.EmailMessage.is_multipart` method will return ``True``.
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The single element yielded by :meth:`~email.message.EmailMessage.iter_parts`
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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.EmailMessage.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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