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c27e52265b
This patch primarily does two things: (1) it adds some internal-interface methods to Policy that allow for Policy to control the parsing and folding of headers in such a way that we can construct a backward compatibility policy that is 100% compatible with the 3.2 API, while allowing a new policy to implement the email6 API. (2) it adds that backward compatibility policy and refactors the test suite so that the only differences between the 3.2 test_email.py file and the 3.3 test_email.py file is some small changes in test framework and the addition of tests for bugs fixed that apply to the 3.2 API. There are some additional teaks, such as moving just the code needed for the compatibility policy into _policybase, so that the library code can import only _policybase. That way the new code that will be added for email6 will only get imported when a non-compatibility policy is imported.
234 lines
11 KiB
ReStructuredText
234 lines
11 KiB
ReStructuredText
:mod:`email`: Generating MIME documents
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---------------------------------------
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.. module:: email.generator
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:synopsis: Generate flat text email messages from a message structure.
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One of the most common tasks is to generate the flat text of the email message
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represented by a message object structure. You will need to do this if you want
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to send your message via the :mod:`smtplib` module or the :mod:`nntplib` module,
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or print the message on the console. Taking a message object structure and
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producing a flat text document is the job of the :class:`Generator` class.
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Again, as with the :mod:`email.parser` module, you aren't limited to the
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functionality of the bundled generator; you could write one from scratch
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yourself. However the bundled generator knows how to generate most email in a
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standards-compliant way, should handle MIME and non-MIME email messages just
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fine, and is designed so that the transformation from flat text, to a message
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structure via the :class:`~email.parser.Parser` class, and back to flat text,
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is idempotent (the input is identical to the output) [#]_. On the other hand,
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using the Generator on a :class:`~email.message.Message` constructed by program
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may result in changes to the :class:`~email.message.Message` object as defaults
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are filled in.
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:class:`bytes` output can be generated using the :class:`BytesGenerator` class.
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If the message object structure contains non-ASCII bytes, this generator's
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:meth:`~BytesGenerator.flatten` method will emit the original bytes. Parsing a
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binary message and then flattening it with :class:`BytesGenerator` should be
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idempotent for standards compliant messages.
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Here are the public methods of the :class:`Generator` class, imported from the
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:mod:`email.generator` module:
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.. class:: Generator(outfp, mangle_from_=True, maxheaderlen=78, *, policy=None)
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The constructor for the :class:`Generator` class takes a :term:`file-like object`
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called *outfp* for an argument. *outfp* must support the :meth:`write` method
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and be usable as the output file for the :func:`print` function.
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Optional *mangle_from_* is a flag that, when ``True``, puts a ``>`` character in
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front of any line in the body that starts exactly as ``From``, i.e. ``From``
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followed by a space at the beginning of the line. This is the only guaranteed
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portable way to avoid having such lines be mistaken for a Unix mailbox format
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envelope header separator (see `WHY THE CONTENT-LENGTH FORMAT IS BAD
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<http://www.jwz.org/doc/content-length.html>`_ for details). *mangle_from_*
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defaults to ``True``, but you might want to set this to ``False`` if you are not
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writing Unix mailbox format files.
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Optional *maxheaderlen* specifies the longest length for a non-continued header.
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When a header line is longer than *maxheaderlen* (in characters, with tabs
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expanded to 8 spaces), the header will be split as defined in the
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:class:`~email.header.Header` class. Set to zero to disable header wrapping.
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The default is 78, as recommended (but not required) by :rfc:`2822`.
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The *policy* keyword specifies a :mod:`~email.policy` object that controls a
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number of aspects of the generator's operation. If no *policy* is specified,
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then the *policy* attached to the message object passed to :attr:``flatten``
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is used.
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.. versionchanged:: 3.3 Added the *policy* keyword.
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The other public :class:`Generator` methods are:
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.. method:: flatten(msg, unixfrom=False, linesep=None)
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Print the textual representation of the message object structure rooted at
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*msg* to the output file specified when the :class:`Generator` instance
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was created. Subparts are visited depth-first and the resulting text will
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be properly MIME encoded.
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Optional *unixfrom* is a flag that forces the printing of the envelope
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header delimiter before the first :rfc:`2822` header of the root message
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object. If the root object has no envelope header, a standard one is
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crafted. By default, this is set to ``False`` to inhibit the printing of
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the envelope delimiter.
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Note that for subparts, no envelope header is ever printed.
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Optional *linesep* specifies the line separator character used to
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terminate lines in the output. If specified it overrides the value
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specified by the *msg*\'s or ``Generator``\'s ``policy``.
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Because strings cannot represent non-ASCII bytes, if the policy that
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applies when ``flatten`` is run has :attr:`~email.policy.Policy.cte_type`
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set to ``8bit``, ``Generator`` will operate as if it were set to
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``7bit``. This means that messages parsed with a Bytes parser that have
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a :mailheader:`Content-Transfer-Encoding` of ``8bit`` will be converted
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to a use a ``7bit`` Content-Transfer-Encoding. Non-ASCII bytes in the
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headers will be :rfc:`2047` encoded with a charset of ``unknown-8bit``.
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.. versionchanged:: 3.2
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Added support for re-encoding ``8bit`` message bodies, and the
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*linesep* argument.
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.. method:: clone(fp)
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Return an independent clone of this :class:`Generator` instance with the
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exact same options.
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.. method:: write(s)
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Write the string *s* to the underlying file object, i.e. *outfp* passed to
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:class:`Generator`'s constructor. This provides just enough file-like API
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for :class:`Generator` instances to be used in the :func:`print` function.
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As a convenience, see the :class:`~email.message.Message` methods
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:meth:`~email.message.Message.as_string` and ``str(aMessage)``, a.k.a.
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:meth:`~email.message.Message.__str__`, which simplify the generation of a
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formatted string representation of a message object. For more detail, see
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:mod:`email.message`.
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.. class:: BytesGenerator(outfp, mangle_from_=True, maxheaderlen=78, *, \
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policy=policy.default)
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The constructor for the :class:`BytesGenerator` class takes a binary
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:term:`file-like object` called *outfp* for an argument. *outfp* must
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support a :meth:`write` method that accepts binary data.
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Optional *mangle_from_* is a flag that, when ``True``, puts a ``>``
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character in front of any line in the body that starts exactly as ``From``,
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i.e. ``From`` followed by a space at the beginning of the line. This is the
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only guaranteed portable way to avoid having such lines be mistaken for a
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Unix mailbox format envelope header separator (see `WHY THE CONTENT-LENGTH
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FORMAT IS BAD <http://www.jwz.org/doc/content-length.html>`_ for details).
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*mangle_from_* defaults to ``True``, but you might want to set this to
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``False`` if you are not writing Unix mailbox format files.
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Optional *maxheaderlen* specifies the longest length for a non-continued
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header. When a header line is longer than *maxheaderlen* (in characters,
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with tabs expanded to 8 spaces), the header will be split as defined in the
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:class:`~email.header.Header` class. Set to zero to disable header
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wrapping. The default is 78, as recommended (but not required) by
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:rfc:`2822`.
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The *policy* keyword specifies a :mod:`~email.policy` object that controls a
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number of aspects of the generator's operation. The default policy
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maintains backward compatibility.
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.. versionchanged:: 3.3 Added the *policy* keyword.
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The other public :class:`BytesGenerator` methods are:
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.. method:: flatten(msg, unixfrom=False, linesep=None)
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Print the textual representation of the message object structure rooted
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at *msg* to the output file specified when the :class:`BytesGenerator`
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instance was created. Subparts are visited depth-first and the resulting
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text will be properly MIME encoded. If the :mod:`~email.policy` option
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:attr:`~email.policy.Policy.cte_type` is ``8bit`` (the default),
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then any bytes with the high bit set in the original parsed message that
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have not been modified will be copied faithfully to the output. If
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``cte_type`` is ``7bit``, the bytes will be converted as needed
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using an ASCII-compatible Content-Transfer-Encoding. In particular,
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RFC-invalid non-ASCII bytes in headers will be encoded using the MIME
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``unknown-8bit`` character set, thus rendering them RFC-compliant.
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.. XXX: There should be a complementary option that just does the RFC
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compliance transformation but leaves CTE 8bit parts alone.
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Messages parsed with a Bytes parser that have a
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:mailheader:`Content-Transfer-Encoding` of 8bit will be reconstructed
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as 8bit if they have not been modified.
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Optional *unixfrom* is a flag that forces the printing of the envelope
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header delimiter before the first :rfc:`2822` header of the root message
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object. If the root object has no envelope header, a standard one is
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crafted. By default, this is set to ``False`` to inhibit the printing of
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the envelope delimiter.
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Note that for subparts, no envelope header is ever printed.
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Optional *linesep* specifies the line separator character used to
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terminate lines in the output. If specified it overrides the value
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specified by the ``Generator``\ 's ``policy``.
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.. method:: clone(fp)
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Return an independent clone of this :class:`BytesGenerator` instance with
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the exact same options.
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.. method:: write(s)
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Write the string *s* to the underlying file object. *s* is encoded using
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the ``ASCII`` codec and written to the *write* method of the *outfp*
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*outfp* passed to the :class:`BytesGenerator`'s constructor. This
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provides just enough file-like API for :class:`BytesGenerator` instances
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to be used in the :func:`print` function.
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.. versionadded:: 3.2
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The :mod:`email.generator` module also provides a derived class, called
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:class:`DecodedGenerator` which is like the :class:`Generator` base class,
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except that non-\ :mimetype:`text` parts are substituted with a format string
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representing the part.
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.. class:: DecodedGenerator(outfp, mangle_from_=True, maxheaderlen=78, fmt=None)
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This class, derived from :class:`Generator` walks through all the subparts of a
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message. If the subpart is of main type :mimetype:`text`, then it prints the
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decoded payload of the subpart. Optional *_mangle_from_* and *maxheaderlen* are
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as with the :class:`Generator` base class.
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If the subpart is not of main type :mimetype:`text`, optional *fmt* is a format
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string that is used instead of the message payload. *fmt* is expanded with the
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following keywords, ``%(keyword)s`` format:
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* ``type`` -- Full MIME type of the non-\ :mimetype:`text` part
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* ``maintype`` -- Main MIME type of the non-\ :mimetype:`text` part
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* ``subtype`` -- Sub-MIME type of the non-\ :mimetype:`text` part
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* ``filename`` -- Filename of the non-\ :mimetype:`text` part
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* ``description`` -- Description associated with the non-\ :mimetype:`text` part
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* ``encoding`` -- Content transfer encoding of the non-\ :mimetype:`text` part
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The default value for *fmt* is ``None``, meaning ::
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[Non-text (%(type)s) part of message omitted, filename %(filename)s]
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.. rubric:: Footnotes
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.. [#] This statement assumes that you use the appropriate setting for the
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``unixfrom`` argument, and that you set maxheaderlen=0 (which will
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preserve whatever the input line lengths were). It is also not strictly
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true, since in many cases runs of whitespace in headers are collapsed
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into single blanks. The latter is a bug that will eventually be fixed.
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