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# 19.1.6. `email.contentmanager`: Managing MIME Content

New in version 3.4: as a provisional module.

Source code: Lib/email/contentmanager.py

Note

The contentmanager module has been included in the standard library on a provisional basis. Backwards incompatible changes (up to and including removal of the module) may occur if deemed necessary by the core developers.

The `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 `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: `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 `Message` that provide new convenience API functions, including convenience methods for calling the Content Managers derived from this module.

Note

Although `EmailMessage` and `MIMEPart` are currently documented in this module because of the provisional nature of the code, the implementation lives in the `email.message` module.

class `email.message.``EmailMessage`(policy=default)

  If policy is specified (it must be an instance of a `policy` class) use the rules it specifies to udpate and serialize the representation of the message. If policy is not set, use the `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 `policy` documentation.

  This class is a subclass of `Message`. It adds the following methods:

  `is_attachment`()

    Return `True` if there is a Content-Disposition header and its (case insensitive) value is `attachment`, `False` otherwise.

    Changed in version 3.4.2: is_attachment is now a method instead of a property, for consistency with `is_multipart()`.

  `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 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 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 Content-Type or whose 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.

  `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 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 Content-ID of any of the parts). When applied directly to a `multipart/alternative` or a non-`multipart`, return an empty iterator.

  `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 `walk()`.)

  `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 `policy`.

  `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 `policy`.

  `make_related`(boundary=None)

    Convert a non-`multipart` message into a `multipart/related` message, moving any existing 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).

  `make_alternative`(boundary=None)

    Convert a non-`multipart` or a `multipart/related` into a `multipart/alternative`, moving any existing 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).

  `make_mixed`(boundary=None)

    Convert a non-`multipart`, a `multipart/related`, or a `multipart-alternative` into a `multipart/mixed`, moving any existing 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).

  `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 `set_content()` method, and `attach()` it to the `multipart`. If the message is a non-`multipart`, call `make_related()` and then proceed as above. If the message is any other type of `multipart`, raise a `TypeError`. If content_manager is not specified, use the `content_manager` specified by the current `policy`. If the added part has no Content-Disposition header, add one with the value `inline`.

  `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 `set_content()` method, and `attach()` it to the `multipart`. If the message is a non-`multipart` or `multipart/related`, call `make_alternative()` and then proceed as above. If the message is any other type of `multipart`, raise a `TypeError`. If content_manager is not specified, use the `content_manager` specified by the current `policy`.

  `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 `set_content()` method, and `attach()` it to the `multipart`. If the message is a non-`multipart`, `multipart/related`, or `multipart/alternative`, call `make_mixed()` and then proceed as above. If content_manager is not specified, use the `content_manager` specified by the current `policy`. If the added part has no Content-Disposition header, add one with the value `attachment`. This method can be used both for explicit attachments (Content-Disposition: attachment and `inline` attachments (Content-Disposition: inline), by passing appropriate options to the `content_manager`.

  `clear`()

    Remove the payload and all of the headers.

  `clear_content`()

    Remove the payload and all of the `Content-` headers, leaving all other headers intact and in their original order.

class `email.message.``MIMEPart`(policy=default)

  This class represents a subpart of a MIME message. It is identical to `EmailMessage`, except that no MIME-Version headers are added when `set_content()` is called, since sub-parts do not need their own MIME-Version headers.

class `email.contentmanager.``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.

  `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 `KeyError` for the full MIME type.

  `set_content`(msg, obj, *args, **kw)

    If the `maintype` is `multipart`, raise a `TypeError`; otherwise look up a handler function based on the type of obj (see next paragraph), call `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 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 `KeyError` for the fully qualified name of the type.

    Also add a MIME-Version header if one is not present (see also `MIMEPart`).

  `add_get_handler`(key, handler)

    Record the function handler as the handler for key. For the possible values of key, see `get_content()`.

  `add_set_handler`(typekey, handler)

    Record handler as the function to call when an object of a type matching typekey is passed to `set_content()`. For the possible values of typekey, see `set_content()`.

## 19.1.6.1. Content Manager Instances

Currently the email package provides only one concrete content manager, `raw_data_manager`, although more may be added in the future. `raw_data_manager` is the `content_manager` provided by `EmailPolicy` and its derivatives.

`email.contentmanager.``raw_data_manager`

  This content manager provides only a minimum interface beyond that provided by `Message` itself: it deals only with text, raw byte strings, and `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.

  `email.contentmanager.``get_content`(msg, errors='replace')

    Return the payload of the part as either a string (for `text` parts), a `EmailMessage` object (for `message/rfc822` parts), or a `bytes` object (for all other non-multipart types). Raise a `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`.

  `email.contentmanager.``set_content`(msg, <'str'>, subtype="plain", charset='utf-8' cte=None, disposition=None, filename=None, cid=None, params=None, headers=None)
  `email.contentmanager.``set_content`(msg, <'bytes'>, maintype, subtype, cte="base64", disposition=None, filename=None, cid=None, params=None, headers=None)
  `email.contentmanager.``set_content`(msg, <'Message'>, cte=None, disposition=None, filename=None, cid=None, params=None, headers=None)
  `email.contentmanager.``set_content`(msg, <'list'>, subtype='mixed', disposition=None, filename=None, cid=None, params=None, headers=None)

    Add headers and payload to msg:

    Add a 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 `TypeError` if they are not specified.
    > - For `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 `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 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 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 `ValueError`. For `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 `BytesGenerator` does not serialize it correctly.

    If disposition is set, use it as the value of the 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 Content-Disposition header. There is no default.

    If cid is specified, add a 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 parameters on the 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.

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