cpython/Doc/library/email.contentmanager.rst

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:mod:`email.contentmanager`: Managing MIME Content
--------------------------------------------------
.. module:: email.contentmanager
:synopsis: Storing and Retrieving Content from MIME Parts
.. moduleauthor:: R. David Murray <rdmurray@bitdance.com>
.. sectionauthor:: R. David Murray <rdmurray@bitdance.com>
.. note::
The contentmanager module has been included in the standard library on a
:term:`provisional basis <provisional package>`. Backwards incompatible
changes (up to and including removal of the module) may occur if deemed
necessary by the core developers.
.. versionadded:: 3.4
as a :term:`provisional module <provisional package>`.
The :mod:`~email.message` module provides a class that can represent an
arbitrary email message. That basic message model has a useful and flexible
API, but it provides only a lower-level API for interacting with the generic
parts of a message (the headers, generic header parameters, and the payload,
which may be a list of sub-parts). This module provides classes and tools
that provide an enhanced and extensible API for dealing with various specific
types of content, including the ability to retrieve the content of the message
as a specialized object type rather than as a simple bytes object. The module
automatically takes care of the RFC-specified MIME details (required headers
and parameters, etc.) for the certain common content types content properties,
and support for additional types can be added by an application using the
extension mechanisms.
This module defines the eponymous "Content Manager" classes. The base
:class:`.ContentManager` class defines an API for registering content
management functions which extract data from ``Message`` objects or insert data
and headers into ``Message`` objects, thus providing a way of converting
between ``Message`` objects containing data and other representations of that
data (Python data types, specialized Python objects, external files, etc). The
module also defines one concrete content manager: :data:`raw_data_manager`
converts between MIME content types and ``str`` or ``bytes`` data. It also
provides a convenient API for managing the MIME parameters when inserting
content into ``Message``\ s. It also handles inserting and extracting
``Message`` objects when dealing with the ``message/rfc822`` content type.
Another part of the enhanced interface is subclasses of
:class:`~email.message.Message` that provide new convenience API functions,
including convenience methods for calling the Content Managers derived from
this module.
.. note::
Although :class:`.EmailMessage` and :class:`.MIMEPart` are currently
documented in this module because of the provisional nature of the code, the
implementation lives in the :mod:`email.message` module.
.. class:: EmailMessage(policy=default)
If *policy* is specified (it must be an instance of a :mod:`~email.policy`
class) use the rules it specifies to udpate and serialize the representation
of the message. If *policy* is not set, use the
:class:`~email.policy.default` policy, which follows the rules of the email
RFCs except for line endings (instead of the RFC mandated ``\r\n``, it uses
the Python standard ``\n`` line endings). For more information see the
:mod:`~email.policy` documentation.
This class is a subclass of :class:`~email.message.Message`. It adds
the following methods:
.. attribute:: is_attachment
Set to ``True`` if there is a :mailheader:`Content-Disposition` header
and its (case insensitive) value is ``attachment``, ``False`` otherwise.
.. method:: get_body(preferencelist=('related', 'html', 'plain'))
Return the MIME part that is the best candidate to be the "body" of the
message.
*preferencelist* must be a sequence of strings from the set ``related``,
``html``, and ``plain``, and indicates the order of preference for the
content type of the part returned.
Start looking for candidate matches with the object on which the
``get_body`` method is called.
If ``related`` is not included in *preferencelist*, consider the root
part (or subpart of the root part) of any related encountered as a
candidate if the (sub-)part matches a preference.
When encountering a ``multipart/related``, check the ``start`` parameter
and if a part with a matching :mailheader:`Content-ID` is found, consider
only it when looking for candidate matches. Otherwise consider only the
first (default root) part of the ``multipart/related``.
If a part has a :mailheader:``Content-Disposition`` header, only consider
the part a candidate match if the value of the header is ``inline``.
If none of the candidates matches any of the preferences in
*preferneclist*, return ``None``.
Notes: (1) For most applications the only *preferencelist* combinations
that really make sense are ``('plain',)``, ``('html', 'plain')``, and the
default, ``('related', 'html', 'plain')``. (2) Because matching starts
with the object on which ``get_body`` is called, calling ``get_body`` on
a ``multipart/related`` will return the object itself unless
*preferencelist* has a non-default value. (3) Messages (or message parts)
that do not specify a :mailheader:`Content-Type` or whose
:mailheader:`Content-Type` header is invalid will be treated as if they
are of type ``text/plain``, which may occasionally cause ``get_body`` to
return unexpected results.
.. method:: iter_attachments()
Return an iterator over all of the parts of the message that are not
candidate "body" parts. That is, skip the first occurrence of each of
``text/plain``, ``text/html``, ``multipart/related``, or
``multipart/alternative`` (unless they are explicitly marked as
attachments via :mailheader:`Content-Disposition: attachment`), and
return all remaining parts. When applied directly to a
``multipart/related``, return an iterator over the all the related parts
except the root part (ie: the part pointed to by the ``start`` parameter,
or the first part if there is no ``start`` parameter or the ``start``
parameter doesn't match the :mailheader:`Content-ID` of any of the
parts). When applied directly to a ``multipart/alternative`` or a
non-``multipart``, return an empty iterator.
.. method:: iter_parts()
Return an iterator over all of the immediate sub-parts of the message,
which will be empty for a non-``multipart``. (See also
:meth:``~email.message.walk``.)
.. method:: get_content(*args, content_manager=None, **kw)
Call the ``get_content`` method of the *content_manager*, passing self
as the message object, and passing along any other arguments or keywords
as additional arguments. If *content_manager* is not specified, use
the ``content_manager`` specified by the current :mod:`~email.policy`.
.. method:: set_content(*args, content_manager=None, **kw)
Call the ``set_content`` method of the *content_manager*, passing self
as the message object, and passing along any other arguments or keywords
as additional arguments. If *content_manager* is not specified, use
the ``content_manager`` specified by the current :mod:`~email.policy`.
.. method:: make_related(boundary=None)
Convert a non-``multipart`` message into a ``multipart/related`` message,
moving any existing :mailheader:`Content-` headers and payload into a
(new) first part of the ``multipart``. If *boundary* is specified, use
it as the boundary string in the multipart, otherwise leave the boundary
to be automatically created when it is needed (for example, when the
message is serialized).
.. method:: make_alternative(boundary=None)
Convert a non-``multipart`` or a ``multipart/related`` into a
``multipart/alternative``, moving any existing :mailheader:`Content-`
headers and payload into a (new) first part of the ``multipart``. If
*boundary* is specified, use it as the boundary string in the multipart,
otherwise leave the boundary to be automatically created when it is
needed (for example, when the message is serialized).
.. method:: make_mixed(boundary=None)
Convert a non-``multipart``, a ``multipart/related``, or a
``multipart-alternative`` into a ``multipart/mixed``, moving any existing
:mailheader:`Content-` headers and payload into a (new) first part of the
``multipart``. If *boundary* is specified, use it as the boundary string
in the multipart, otherwise leave the boundary to be automatically
created when it is needed (for example, when the message is serialized).
.. method:: add_related(*args, content_manager=None, **kw)
If the message is a ``multipart/related``, create a new message
object, pass all of the arguments to its :meth:`set_content` method,
and :meth:`~email.message.Message.attach` it to the ``multipart``. If
the message is a non-``multipart``, call :meth:`make_related` and then
proceed as above. If the message is any other type of ``multipart``,
raise a :exc:`TypeError`. If *content_manager* is not specified, use
the ``content_manager`` specified by the current :mod:`~email.policy`.
If the added part has no :mailheader:`Content-Disposition` header,
add one with the value ``inline``.
.. method:: add_alternative(*args, content_manager=None, **kw)
If the message is a ``multipart/alternative``, create a new message
object, pass all of the arguments to its :meth:`set_content` method, and
:meth:`~email.message.Message.attach` it to the ``multipart``. If the
message is a non-``multipart`` or ``multipart/related``, call
:meth:`make_alternative` and then proceed as above. If the message is
any other type of ``multipart``, raise a :exc:`TypeError`. If
*content_manager* is not specified, use the ``content_manager`` specified
by the current :mod:`~email.policy`.
.. method:: add_attachment(*args, content_manager=None, **kw)
If the message is a ``multipart/mixed``, create a new message object,
pass all of the arguments to its :meth:`set_content` method, and
:meth:`~email.message.Message.attach` it to the ``multipart``. If the
message is a non-``multipart``, ``multipart/related``, or
``multipart/alternative``, call :meth:`make_mixed` and then proceed as
above. If *content_manager* is not specified, use the ``content_manager``
specified by the current :mod:`~email.policy`. If the added part
has no :mailheader:`Content-Disposition` header, add one with the value
``attachment``. This method can be used both for explicit attachments
(:mailheader:`Content-Disposition: attachment` and ``inline`` attachments
(:mailheader:`Content-Disposition: inline`), by passing appropriate
options to the ``content_manager``.
.. method:: clear()
Remove the payload and all of the headers.
.. method:: clear_content()
Remove the payload and all of the :exc:`Content-` headers, leaving
all other headers intact and in their original order.
.. class:: ContentManager()
Base class for content managers. Provides the standard registry mechanisms
to register converters between MIME content and other representations, as
well as the ``get_content`` and ``set_content`` dispatch methods.
.. method:: get_content(msg, *args, **kw)
Look up a handler function based on the ``mimetype`` of *msg* (see next
paragraph), call it, passing through all arguments, and return the result
of the call. The expectation is that the handler will extract the
payload from *msg* and return an object that encodes information about
the extracted data.
To find the handler, look for the following keys in the registry,
stopping with the first one found:
* the string representing the full MIME type (``maintype/subtype``)
* the string representing the ``maintype``
* the empty string
If none of these keys produce a handler, raise a :exc:`KeyError` for the
full MIME type.
.. method:: set_content(msg, obj, *args, **kw)
If the ``maintype`` is ``multipart``, raise a :exc:`TypeError`; otherwise
look up a handler function based on the type of *obj* (see next
paragraph), call :meth:`~email.message.EmailMessage.clear_content` on the
*msg*, and call the handler function, passing through all arguments. The
expectation is that the handler will transform and store *obj* into
*msg*, possibly making other changes to *msg* as well, such as adding
various MIME headers to encode information needed to interpret the stored
data.
To find the handler, obtain the type of *obj* (``typ = type(obj)``), and
look for the following keys in the registry, stopping with the first one
found:
* the type itself (``typ``)
* the type's fully qualified name (``typ.__module__ + '.' +
typ.__qualname__``).
* the type's qualname (``typ.__qualname__``)
* the type's name (``typ.__name__``).
If none of the above match, repeat all of the checks above for each of
the types in the :term:`MRO` (``typ.__mro__``). Finally, if no other key
yields a handler, check for a handler for the key ``None``. If there is
no handler for ``None``, raise a :exc:`KeyError` for the fully
qualified name of the type.
Also add a :mailheader:`MIME-Version` header if one is not present (see
also :class:`.MIMEPart`).
.. method:: add_get_handler(key, handler)
Record the function *handler* as the handler for *key*. For the possible
values of *key*, see :meth:`get_content`.
.. method:: add_set_handler(typekey, handler)
Record *handler* as the function to call when an object of a type
matching *typekey* is passed to :meth:`set_content`. For the possible
values of *typekey*, see :meth:`set_content`.
.. class:: MIMEPart(policy=default)
This class represents a subpart of a MIME message. It is identical to
:class:`EmailMessage`, except that no :mailheader:`MIME-Version` headers are
added when :meth:`~EmailMessage.set_content` is called, since sub-parts do
not need their own :mailheader:`MIME-Version` headers.
Content Manager Instances
~~~~~~~~~~~~~~~~~~~~~~~~~
Currently the email package provides only one concrete content manager,
:data:`raw_data_manager`, although more may be added in the future.
:data:`raw_data_manager` is the
:attr:`~email.policy.EmailPolicy.content_manager` provided by
:attr:`~email.policy.EmailPolicy` and its derivatives.
.. data:: raw_data_manager
This content manager provides only a minimum interface beyond that provided
by :class:`~email.message.Message` itself: it deals only with text, raw
byte strings, and :class:`~email.message.Message` objects. Nevertheless, it
provides significant advantages compared to the base API: ``get_content`` on
a text part will return a unicode string without the application needing to
manually decode it, ``set_content`` provides a rich set of options for
controlling the headers added to a part and controlling the content transfer
encoding, and it enables the use of the various ``add_`` methods, thereby
simplifying the creation of multipart messages.
.. method:: get_content(msg, errors='replace')
Return the payload of the part as either a string (for ``text`` parts), a
:class:`~email.message.EmailMessage` object (for ``message/rfc822``
parts), or a ``bytes`` object (for all other non-multipart types). Raise
a :exc:`KeyError` if called on a ``multipart``. If the part is a
``text`` part and *errors* is specified, use it as the error handler when
decoding the payload to unicode. The default error handler is
``replace``.
.. method:: set_content(msg, <'str'>, subtype="plain", charset='utf-8' \
cte=None, \
disposition=None, filename=None, cid=None, \
params=None, headers=None)
set_content(msg, <'bytes'>, maintype, subtype, cte="base64", \
disposition=None, filename=None, cid=None, \
params=None, headers=None)
set_content(msg, <'Message'>, cte=None, \
disposition=None, filename=None, cid=None, \
params=None, headers=None)
set_content(msg, <'list'>, subtype='mixed', \
disposition=None, filename=None, cid=None, \
params=None, headers=None)
Add headers and payload to *msg*:
Add a :mailheader:`Content-Type` header with a ``maintype/subtype``
value.
* For ``str``, set the MIME ``maintype`` to ``text``, and set the
subtype to *subtype* if it is specified, or ``plain`` if it is not.
* For ``bytes``, use the specified *maintype* and *subtype*, or
raise a :exc:`TypeError` if they are not specified.
* For :class:`~email.message.Message` objects, set the maintype to
``message``, and set the subtype to *subtype* if it is specified
or ``rfc822`` if it is not. If *subtype* is ``partial``, raise an
error (``bytes`` objects must be used to construct
``message/partial`` parts).
* For *<'list'>*, which should be a list of
:class:`~email.message.Message` objects, set the ``maintype`` to
``multipart``, and the ``subtype`` to *subtype* if it is
specified, and ``mixed`` if it is not. If the message parts in
the *<'list'>* have :mailheader:`MIME-Version` headers, remove
them.
If *charset* is provided (which is valid only for ``str``), encode the
string to bytes using the specified character set. The default is
``utf-8``. If the specified *charset* is a known alias for a standard
MIME charset name, use the standard charset instead.
If *cte* is set, encode the payload using the specified content transfer
encoding, and set the :mailheader:`Content-Transfer-Endcoding` header to
that value. For ``str`` objects, if it is not set use heuristics to
determine the most compact encoding. Possible values for *cte* are
``quoted-printable``, ``base64``, ``7bit``, ``8bit``, and ``binary``.
If the input cannot be encoded in the specified encoding (eg: ``7bit``),
raise a :exc:`ValueError`. For :class:`~email.message.Message`, per
:rfc:`2046`, raise an error if a *cte* of ``quoted-printable`` or
``base64`` is requested for *subtype* ``rfc822``, and for any *cte*
other than ``7bit`` for *subtype* ``external-body``. For
``message/rfc822``, use ``8bit`` if *cte* is not specified. For all
other values of *subtype*, use ``7bit``.
.. note:: A *cte* of ``binary`` does not actually work correctly yet.
The ``Message`` object as modified by ``set_content`` is correct, but
:class:`~email.generator.BytesGenerator` does not serialize it
correctly.
If *disposition* is set, use it as the value of the
:mailheader:`Content-Disposition` header. If not specified, and
*filename* is specified, add the header with the value ``attachment``.
If it is not specified and *filename* is also not specified, do not add
the header. The only valid values for *disposition* are ``attachment``
and ``inline``.
If *filename* is specified, use it as the value of the ``filename``
parameter of the :mailheader:`Content-Disposition` header. There is no
default.
If *cid* is specified, add a :mailheader:`Content-ID` header with
*cid* as its value.
If *params* is specified, iterate its ``items`` method and use the
resulting ``(key, value)`` pairs to set additional paramters on the
:mailheader:`Content-Type` header.
If *headers* is specified and is a list of strings of the form
``headername: headervalue`` or a list of ``header`` objects
(distinguised from strings by having a ``name`` attribute), add the
headers to *msg*.