/Doc/library/email.message.rst
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- :mod:`email`: Representing an email message
- -------------------------------------------
- .. module:: email.message
- :synopsis: The base class representing email messages.
- The central class in the :mod:`email` package is the :class:`Message` class,
- imported from the :mod:`email.message` module. It is the base class for the
- :mod:`email` object model. :class:`Message` provides the core functionality for
- setting and querying header fields, and for accessing message bodies.
- Conceptually, a :class:`Message` object consists of *headers* and *payloads*.
- Headers are :rfc:`2822` style field names and values where the field name and
- value are separated by a colon. The colon is not part of either the field name
- or the field value.
- Headers are stored and returned in case-preserving form but are matched
- case-insensitively. There may also be a single envelope header, also known as
- the *Unix-From* header or the ``From_`` header. The payload is either a string
- in the case of simple message objects or a list of :class:`Message` objects for
- MIME container documents (e.g. :mimetype:`multipart/\*` and
- :mimetype:`message/rfc822`).
- :class:`Message` objects provide a mapping style interface for accessing the
- message headers, and an explicit interface for accessing both the headers and
- the payload. It provides convenience methods for generating a flat text
- representation of the message object tree, for accessing commonly used header
- parameters, and for recursively walking over the object tree.
- Here are the methods of the :class:`Message` class:
- .. class:: Message()
- The constructor takes no arguments.
- .. method:: as_string([unixfrom])
- Return the entire message flattened as a string. When optional *unixfrom*
- is ``True``, the envelope header is included in the returned string.
- *unixfrom* defaults to ``False``.
- Note that this method is provided as a convenience and may not always
- format the message the way you want. For example, by default it mangles
- lines that begin with ``From``. For more flexibility, instantiate a
- :class:`~email.generator.Generator` instance and use its :meth:`flatten`
- method directly. For example::
- from cStringIO import StringIO
- from email.generator import Generator
- fp = StringIO()
- g = Generator(fp, mangle_from_=False, maxheaderlen=60)
- g.flatten(msg)
- text = fp.getvalue()
- .. method:: __str__()
- Equivalent to ``as_string(unixfrom=True)``.
- .. method:: is_multipart()
- Return ``True`` if the message's payload is a list of sub-\
- :class:`Message` objects, otherwise return ``False``. When
- :meth:`is_multipart` returns False, the payload should be a string object.
- .. method:: set_unixfrom(unixfrom)
- Set the message's envelope header to *unixfrom*, which should be a string.
- .. method:: get_unixfrom()
- Return the message's envelope header. Defaults to ``None`` if the
- envelope header was never set.
- .. method:: attach(payload)
- Add the given *payload* to the current payload, which must be ``None`` or
- a list of :class:`Message` objects before the call. After the call, the
- payload will always be a list of :class:`Message` objects. If you want to
- set the payload to a scalar object (e.g. a string), use
- :meth:`set_payload` instead.
- .. method:: get_payload([i[, decode]])
- Return the current payload, which will be a list of
- :class:`Message` objects when :meth:`is_multipart` is ``True``, or a
- string when :meth:`is_multipart` is ``False``. If the payload is a list
- and you mutate the list object, you modify the message's payload in place.
- With optional argument *i*, :meth:`get_payload` will return the *i*-th
- element of the payload, counting from zero, if :meth:`is_multipart` is
- ``True``. An :exc:`IndexError` will be raised if *i* is less than 0 or
- greater than or equal to the number of items in the payload. If the
- payload is a string (i.e. :meth:`is_multipart` is ``False``) and *i* is
- given, a :exc:`TypeError` is raised.
- Optional *decode* is a flag indicating whether the payload should be
- decoded or not, according to the :mailheader:`Content-Transfer-Encoding`
- header. When ``True`` and the message is not a multipart, the payload will
- be decoded if this header's value is ``quoted-printable`` or ``base64``.
- If some other encoding is used, or :mailheader:`Content-Transfer-Encoding`
- header is missing, or if the payload has bogus base64 data, the payload is
- returned as-is (undecoded). If the message is a multipart and the
- *decode* flag is ``True``, then ``None`` is returned. The default for
- *decode* is ``False``.
- .. method:: set_payload(payload[, charset])
- Set the entire message object's payload to *payload*. It is the client's
- responsibility to ensure the payload invariants. Optional *charset* sets
- the message's default character set; see :meth:`set_charset` for details.
- .. versionchanged:: 2.2.2
- *charset* argument added.
- .. method:: set_charset(charset)
- Set the character set of the payload to *charset*, which can either be a
- :class:`~email.charset.Charset` instance (see :mod:`email.charset`), a
- string naming a character set, or ``None``. If it is a string, it will
- be converted to a :class:`~email.charset.Charset` instance. If *charset*
- is ``None``, the ``charset`` parameter will be removed from the
- :mailheader:`Content-Type` header. Anything else will generate a
- :exc:`TypeError`.
- The message will be assumed to be of type :mimetype:`text/\*` encoded with
- *charset.input_charset*. It will be converted to *charset.output_charset*
- and encoded properly, if needed, when generating the plain text
- representation of the message. MIME headers (:mailheader:`MIME-Version`,
- :mailheader:`Content-Type`, :mailheader:`Content-Transfer-Encoding`) will
- be added as needed.
- .. versionadded:: 2.2.2
- .. method:: get_charset()
- Return the :class:`~email.charset.Charset` instance associated with the
- message's payload.
- .. versionadded:: 2.2.2
- The following methods implement a mapping-like interface for accessing the
- message's :rfc:`2822` headers. Note that there are some semantic differences
- between these methods and a normal mapping (i.e. dictionary) interface. For
- example, in a dictionary there are no duplicate keys, but here there may be
- duplicate message headers. Also, in dictionaries there is no guaranteed
- order to the keys returned by :meth:`keys`, but in a :class:`Message` object,
- headers are always returned in the order they appeared in the original
- message, or were added to the message later. Any header deleted and then
- re-added are always appended to the end of the header list.
- These semantic differences are intentional and are biased toward maximal
- convenience.
- Note that in all cases, any envelope header present in the message is not
- included in the mapping interface.
- .. method:: __len__()
- Return the total number of headers, including duplicates.
- .. method:: __contains__(name)
- Return true if the message object has a field named *name*. Matching is
- done case-insensitively and *name* should not include the trailing colon.
- Used for the ``in`` operator, e.g.::
- if 'message-id' in myMessage:
- print 'Message-ID:', myMessage['message-id']
- .. method:: __getitem__(name)
- Return the value of the named header field. *name* should not include the
- colon field separator. If the header is missing, ``None`` is returned; a
- :exc:`KeyError` is never raised.
- Note that if the named field appears more than once in the message's
- headers, exactly which of those field values will be returned is
- undefined. Use the :meth:`get_all` method to get the values of all the
- extant named headers.
- .. method:: __setitem__(name, val)
- Add a header to the message with field name *name* and value *val*. The
- field is appended to the end of the message's existing fields.
- Note that this does *not* overwrite or delete any existing header with the same
- name. If you want to ensure that the new header is the only one present in the
- message with field name *name*, delete the field first, e.g.::
- del msg['subject']
- msg['subject'] = 'Python roolz!'
- .. method:: __delitem__(name)
- Delete all occurrences of the field with name *name* from the message's
- headers. No exception is raised if the named field isn't present in the headers.
- .. method:: has_key(name)
- Return true if the message contains a header field named *name*, otherwise
- return false.
- .. method:: keys()
- Return a list of all the message's header field names.
- .. method:: values()
- Return a list of all the message's field values.
- .. method:: items()
- Return a list of 2-tuples containing all the message's field headers and
- values.
- .. method:: get(name[, failobj])
- Return the value of the named header field. This is identical to
- :meth:`__getitem__` except that optional *failobj* is returned if the
- named header is missing (defaults to ``None``).
- Here are some additional useful methods:
- .. method:: get_all(name[, failobj])
- Return a list of all the values for the field named *name*. If there are
- no such named headers in the message, *failobj* is returned (defaults to
- ``None``).
- .. method:: add_header(_name, _value, **_params)
- Extended header setting. This method is similar to :meth:`__setitem__`
- except that additional header parameters can be provided as keyword
- arguments. *_name* is the header field to add and *_value* is the
- *primary* value for the header.
- For each item in the keyword argument dictionary *_params*, the key is
- taken as the parameter name, with underscores converted to dashes (since
- dashes are illegal in Python identifiers). Normally, the parameter will
- be added as ``key="value"`` unless the value is ``None``, in which case
- only the key will be added.
- Here's an example::
- msg.add_header('Content-Disposition', 'attachment', filename='bud.gif')
- This will add a header that looks like ::
- Content-Disposition: attachment; filename="bud.gif"
- .. method:: replace_header(_name, _value)
- Replace a header. Replace the first header found in the message that
- matches *_name*, retaining header order and field name case. If no
- matching header was found, a :exc:`KeyError` is raised.
- .. versionadded:: 2.2.2
- .. method:: get_content_type()
- Return the message's content type. The returned string is coerced to
- lower case of the form :mimetype:`maintype/subtype`. If there was no
- :mailheader:`Content-Type` header in the message the default type as given
- by :meth:`get_default_type` will be returned. Since according to
- :rfc:`2045`, messages always have a default type, :meth:`get_content_type`
- will always return a value.
- :rfc:`2045` defines a message's default type to be :mimetype:`text/plain`
- unless it appears inside a :mimetype:`multipart/digest` container, in
- which case it would be :mimetype:`message/rfc822`. If the
- :mailheader:`Content-Type` header has an invalid type specification,
- :rfc:`2045` mandates that the default type be :mimetype:`text/plain`.
- .. versionadded:: 2.2.2
- .. method:: get_content_maintype()
- Return the message's main content type. This is the :mimetype:`maintype`
- part of the string returned by :meth:`get_content_type`.
- .. versionadded:: 2.2.2
- .. method:: get_content_subtype()
- Return the message's sub-content type. This is the :mimetype:`subtype`
- part of the string returned by :meth:`get_content_type`.
- .. versionadded:: 2.2.2
- .. method:: get_default_type()
- Return the default content type. Most messages have a default content
- type of :mimetype:`text/plain`, except for messages that are subparts of
- :mimetype:`multipart/digest` containers. Such subparts have a default
- content type of :mimetype:`message/rfc822`.
- .. versionadded:: 2.2.2
- .. method:: set_default_type(ctype)
- Set the default content type. *ctype* should either be
- :mimetype:`text/plain` or :mimetype:`message/rfc822`, although this is not
- enforced. The default content type is not stored in the
- :mailheader:`Content-Type` header.
- .. versionadded:: 2.2.2
- .. method:: get_params([failobj[, header[, unquote]]])
- Return the message's :mailheader:`Content-Type` parameters, as a list.
- The elements of the returned list are 2-tuples of key/value pairs, as
- split on the ``'='`` sign. The left hand side of the ``'='`` is the key,
- while the right hand side is the value. If there is no ``'='`` sign in
- the parameter the value is the empty string, otherwise the value is as
- described in :meth:`get_param` and is unquoted if optional *unquote* is
- ``True`` (the default).
- Optional *failobj* is the object to return if there is no
- :mailheader:`Content-Type` header. Optional *header* is the header to
- search instead of :mailheader:`Content-Type`.
- .. versionchanged:: 2.2.2
- *unquote* argument added.
- .. method:: get_param(param[, failobj[, header[, unquote]]])
- Return the value of the :mailheader:`Content-Type` header's parameter
- *param* as a string. If the message has no :mailheader:`Content-Type`
- header or if there is no such parameter, then *failobj* is returned
- (defaults to ``None``).
- Optional *header* if given, specifies the message header to use instead of
- :mailheader:`Content-Type`.
- Parameter keys are always compared case insensitively. The return value
- can either be a string, or a 3-tuple if the parameter was :rfc:`2231`
- encoded. When it's a 3-tuple, the elements of the value are of the form
- ``(CHARSET, LANGUAGE, VALUE)``. Note that both ``CHARSET`` and
- ``LANGUAGE`` can be ``None``, in which case you should consider ``VALUE``
- to be encoded in the ``us-ascii`` charset. You can usually ignore
- ``LANGUAGE``.
- If your application doesn't care whether the parameter was encoded as in
- :rfc:`2231`, you can collapse the parameter value by calling
- :func:`email.utils.collapse_rfc2231_value`, passing in the return value
- from :meth:`get_param`. This will return a suitably decoded Unicode
- string whn the value is a tuple, or the original string unquoted if it
- isn't. For example::
- rawparam = msg.get_param('foo')
- param = email.utils.collapse_rfc2231_value(rawparam)
- In any case, the parameter value (either the returned string, or the
- ``VALUE`` item in the 3-tuple) is always unquoted, unless *unquote* is set
- to ``False``.
- .. versionchanged:: 2.2.2
- *unquote* argument added, and 3-tuple return value possible.
- .. method:: set_param(param, value[, header[, requote[, charset[, language]]]])
- Set a parameter in the :mailheader:`Content-Type` header. If the
- parameter already exists in the header, its value will be replaced with
- *value*. If the :mailheader:`Content-Type` header as not yet been defined
- for this message, it will be set to :mimetype:`text/plain` and the new
- parameter value will be appended as per :rfc:`2045`.
- Optional *header* specifies an alternative header to
- :mailheader:`Content-Type`, and all parameters will be quoted as necessary
- unless optional *requote* is ``False`` (the default is ``True``).
- If optional *charset* is specified, the parameter will be encoded
- according to :rfc:`2231`. Optional *language* specifies the RFC 2231
- language, defaulting to the empty string. Both *charset* and *language*
- should be strings.
- .. versionadded:: 2.2.2
- .. method:: del_param(param[, header[, requote]])
- Remove the given parameter completely from the :mailheader:`Content-Type`
- header. The header will be re-written in place without the parameter or
- its value. All values will be quoted as necessary unless *requote* is
- ``False`` (the default is ``True``). Optional *header* specifies an
- alternative to :mailheader:`Content-Type`.
- .. versionadded:: 2.2.2
- .. method:: set_type(type[, header][, requote])
- Set the main type and subtype for the :mailheader:`Content-Type`
- header. *type* must be a string in the form :mimetype:`maintype/subtype`,
- otherwise a :exc:`ValueError` is raised.
- This method replaces the :mailheader:`Content-Type` header, keeping all
- the parameters in place. If *requote* is ``False``, this leaves the
- existing header's quoting as is, otherwise the parameters will be quoted
- (the default).
- An alternative header can be specified in the *header* argument. When the
- :mailheader:`Content-Type` header is set a :mailheader:`MIME-Version`
- header is also added.
- .. versionadded:: 2.2.2
- .. method:: get_filename([failobj])
- Return the value of the ``filename`` parameter of the
- :mailheader:`Content-Disposition` header of the message. If the header
- does not have a ``filename`` parameter, this method falls back to looking
- for the ``name`` parameter. If neither is found, or the header is
- missing, then *failobj* is returned. The returned string will always be
- unquoted as per :func:`email.utils.unquote`.
- .. method:: get_boundary([failobj])
- Return the value of the ``boundary`` parameter of the
- :mailheader:`Content-Type` header of the message, or *failobj* if either
- the header is missing, or has no ``boundary`` parameter. The returned
- string will always be unquoted as per :func:`email.utils.unquote`.
- .. method:: set_boundary(boundary)
- Set the ``boundary`` parameter of the :mailheader:`Content-Type` header to
- *boundary*. :meth:`set_boundary` will always quote *boundary* if
- necessary. A :exc:`HeaderParseError` is raised if the message object has
- no :mailheader:`Content-Type` header.
- Note that using this method is subtly different than deleting the old
- :mailheader:`Content-Type` header and adding a new one with the new
- boundary via :meth:`add_header`, because :meth:`set_boundary` preserves
- the order of the :mailheader:`Content-Type` header in the list of
- headers. However, it does *not* preserve any continuation lines which may
- have been present in the original :mailheader:`Content-Type` header.
- .. method:: get_content_charset([failobj])
- Return the ``charset`` parameter of the :mailheader:`Content-Type` header,
- coerced to lower case. If there is no :mailheader:`Content-Type` header, or if
- that header has no ``charset`` parameter, *failobj* is returned.
- Note that this method differs from :meth:`get_charset` which returns the
- :class:`~email.charset.Charset` instance for the default encoding of the message body.
- .. versionadded:: 2.2.2
- .. method:: get_charsets([failobj])
- Return a list containing the character set names in the message. If the
- message is a :mimetype:`multipart`, then the list will contain one element
- for each subpart in the payload, otherwise, it will be a list of length 1.
- Each item in the list will be a string which is the value of the
- ``charset`` parameter in the :mailheader:`Content-Type` header for the
- represented subpart. However, if the subpart has no
- :mailheader:`Content-Type` header, no ``charset`` parameter, or is not of
- the :mimetype:`text` main MIME type, then that item in the returned list
- will be *failobj*.
- .. method:: walk()
- The :meth:`walk` method is an all-purpose generator which can be used to
- iterate over all the parts and subparts of a message object tree, in
- depth-first traversal order. You will typically use :meth:`walk` as the
- iterator in a ``for`` loop; each iteration returns the next subpart.
- Here's an example that prints the MIME type of every part of a multipart
- message structure::
- >>> for part in msg.walk():
- ... print part.get_content_type()
- multipart/report
- text/plain
- message/delivery-status
- text/plain
- text/plain
- message/rfc822
- .. versionchanged:: 2.5
- The previously deprecated methods :meth:`get_type`, :meth:`get_main_type`, and
- :meth:`get_subtype` were removed.
- :class:`Message` objects can also optionally contain two instance attributes,
- which can be used when generating the plain text of a MIME message.
- .. attribute:: preamble
- The format of a MIME document allows for some text between the blank line
- following the headers, and the first multipart boundary string. Normally,
- this text is never visible in a MIME-aware mail reader because it falls
- outside the standard MIME armor. However, when viewing the raw text of
- the message, or when viewing the message in a non-MIME aware reader, this
- text can become visible.
- The *preamble* attribute contains this leading extra-armor text for MIME
- documents. When the :class:`~email.parser.Parser` discovers some text
- after the headers but before the first boundary string, it assigns this
- text to the message's *preamble* attribute. When the
- :class:`~email.generator.Generator` is writing out the plain text
- representation of a MIME message, and it finds the
- message has a *preamble* attribute, it will write this text in the area
- between the headers and the first boundary. See :mod:`email.parser` and
- :mod:`email.generator` for details.
- Note that if the message object has no preamble, the *preamble* attribute
- will be ``None``.
- .. attribute:: epilogue
- The *epilogue* attribute acts the same way as the *preamble* attribute,
- except that it contains text that appears between the last boundary and
- the end of the message.
- .. versionchanged:: 2.5
- You do not need to set the epilogue to the empty string in order for the
- :class:`Generator` to print a newline at the end of the file.
- .. attribute:: defects
- The *defects* attribute contains a list of all the problems found when
- parsing this message. See :mod:`email.errors` for a detailed description
- of the possible parsing defects.
- .. versionadded:: 2.4