19.1.6. email.contentmanager: Managing MIME Content

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 Messages. 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.

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

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

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().