19.1. "email" — An email and MIME handling package
**************************************************

**Source code:** Lib/email/__init__.py

======================================================================

The "email" package is a library for managing email messages,
including MIME and other **RFC 2822**-based message documents.  It is
specifically *not* designed to do any sending of email messages to
SMTP (**RFC 2821**), NNTP, or other servers; those are functions of
modules such as "smtplib" and "nntplib". The "email" package attempts
to be as RFC-compliant as possible, supporting in addition to **RFC
2822**, such MIME-related RFCs as **RFC 2045**, **RFC 2046**, **RFC
2047**, and **RFC 2231**.

The primary distinguishing feature of the "email" package is that it
splits the parsing and generating of email messages from the internal
*object model* representation of email.  Applications using the
"email" package deal primarily with objects; you can add sub-objects
to messages, remove sub-objects from messages, completely re-arrange
the contents, etc.  There is a separate parser and a separate
generator which handles the transformation from flat text to the
object model, and then back to flat text again.  There are also handy
subclasses for some common MIME object types, and a few miscellaneous
utilities that help with such common tasks as extracting and parsing
message field values, creating RFC-compliant dates, etc.

The following sections describe the functionality of the "email"
package. The ordering follows a progression that should be common in
applications: an email message is read as flat text from a file or
other source, the text is parsed to produce the object structure of
the email message, this structure is manipulated, and finally, the
object tree is rendered back into flat text.

It is perfectly feasible to create the object structure out of whole
cloth — i.e. completely from scratch.  From there, a similar
progression can be taken as above.

Also included are detailed specifications of all the classes and
modules that the "email" package provides, the exception classes you
might encounter while using the "email" package, some auxiliary
utilities, and a few examples.  For users of the older "mimelib"
package, or previous versions of the "email" package, a section on
differences and porting is provided.

Contents of the "email" package documentation:

* 19.1.1. "email.message": Representing an email message

* 19.1.2. "email.parser": Parsing email messages

  * 19.1.2.1. FeedParser API

  * 19.1.2.2. Parser class API

  * 19.1.2.3. Additional notes

* 19.1.3. "email.generator": Generating MIME documents

* 19.1.4. "email.policy": Policy Objects

* 19.1.5. "email.headerregistry": Custom Header Objects

* 19.1.6. "email.contentmanager": Managing MIME Content

  * 19.1.6.1. Content Manager Instances

* 19.1.7. "email.mime": Creating email and MIME objects from scratch

* 19.1.8. "email.header": Internationalized headers

* 19.1.9. "email.charset": Representing character sets

* 19.1.10. "email.encoders": Encoders

* 19.1.11. "email.errors": Exception and Defect classes

* 19.1.12. "email.utils": Miscellaneous utilities

* 19.1.13. "email.iterators": Iterators

* 19.1.14. "email": Examples

  * 19.1.14.1. Examples using the Provisional API

See also:

  Module "smtplib"
     SMTP protocol client

  Module "nntplib"
     NNTP protocol client


19.1.15. Package History
========================

This table describes the release history of the email package,
corresponding to the version of Python that the package was released
with.  For purposes of this document, when you see a note about change
or added versions, these refer to the Python version the change was
made in, *not* the email package version.  This table also describes
the Python compatibility of each version of the package.

+-----------------+--------------------------------+-------------------------+
| email version   | distributed with               | compatible with         |
+=================+================================+=========================+
| "1.x"           | Python 2.2.0 to Python 2.2.1   | *no longer supported*   |
+-----------------+--------------------------------+-------------------------+
| "2.5"           | Python 2.2.2+ and Python 2.3   | Python 2.1 to 2.5       |
+-----------------+--------------------------------+-------------------------+
| "3.0"           | Python 2.4 and Python 2.5      | Python 2.3 to 2.6       |
+-----------------+--------------------------------+-------------------------+
| "4.0"           | Python 2.5 to Python 2.7       | Python 2.3 to 2.7       |
+-----------------+--------------------------------+-------------------------+
| "5.0"           | Python 3.0 and Python 3.1      | Python 3.0 to 3.2       |
+-----------------+--------------------------------+-------------------------+
| "5.1"           | Python 3.2                     | Python 3.2              |
+-----------------+--------------------------------+-------------------------+

After Version 5.1 (Python 3.2), the email package no longer has a
version that is separate from the Python version.  (See the What’s New
in Python documents for the respective Python versions for details on
changes.)

Here are the major differences between "email" version 5.1 and version
5.0:

* It is once again possible to parse messages containing non-ASCII
  bytes, and to reproduce such messages if the data containing the
  non-ASCII bytes is not modified.

* New functions "message_from_bytes()" and
  "message_from_binary_file()", and new classes "BytesFeedParser" and
  "BytesParser" allow binary message data to be parsed into model
  objects.

* Given bytes input to the model, "get_payload()" will by default
  decode a message body that has a *Content-Transfer-Encoding* of
  "8bit" using the charset specified in the MIME headers and return
  the resulting string.

* Given bytes input to the model, "Generator" will convert message
  bodies that have a *Content-Transfer-Encoding* of 8bit to instead
  have a 7bit Content-Transfer-Encoding.

* New class "BytesGenerator" produces bytes as output, preserving
  any unchanged non-ASCII data that was present in the input used to
  build the model, including message bodies with a *Content-Transfer-
  Encoding* of 8bit.

Here are the major differences between "email" version 5.0 and version
4:

* All operations are on unicode strings.  Text inputs must be
  strings, text outputs are strings.  Outputs are limited to the ASCII
  character set and so can be encoded to ASCII for transmission.
  Inputs are also limited to ASCII; this is an acknowledged limitation
  of email 5.0 and means it can only be used to parse email that is
  7bit clean.

Here are the major differences between "email" version 4 and version
3:

* All modules have been renamed according to **PEP 8** standards.
  For example, the version 3 module "email.Message" was renamed to
  "email.message" in version 4.

* A new subpackage "email.mime" was added and all the version 3
  "email.MIME*" modules were renamed and situated into the
  "email.mime" subpackage.  For example, the version 3 module
  "email.MIMEText" was renamed to "email.mime.text".

  *Note that the version 3 names will continue to work until Python
  2.6*.

* The "email.mime.application" module was added, which contains the
  "MIMEApplication" class.

* Methods that were deprecated in version 3 have been removed.
  These include "Generator.__call__()", "Message.get_type()",
  "Message.get_main_type()", "Message.get_subtype()".

* Fixes have been added for **RFC 2231** support which can change
  some of the return types for "Message.get_param" and friends.  Under
  some circumstances, values which used to return a 3-tuple now return
  simple strings (specifically, if all extended parameter segments
  were unencoded, there is no language and charset designation
  expected, so the return type is now a simple string).  Also,
  %-decoding used to be done for both encoded and unencoded segments;
  this decoding is now done only for encoded segments.

Here are the major differences between "email" version 3 and version
2:

* The "FeedParser" class was introduced, and the "Parser" class was
  implemented in terms of the "FeedParser".  All parsing therefore is
  non-strict, and parsing will make a best effort never to raise an
  exception. Problems found while parsing messages are stored in the
  message’s *defect* attribute.

* All aspects of the API which raised "DeprecationWarning"s in
  version 2 have been removed.  These include the *_encoder* argument
  to the "MIMEText" constructor, the "Message.add_payload()" method,
  the "Utils.dump_address_pair()" function, and the functions
  "Utils.decode()" and "Utils.encode()".

* New "DeprecationWarning"s have been added to:
  "Generator.__call__()", "Message.get_type()",
  "Message.get_main_type()", "Message.get_subtype()", and the *strict*
  argument to the "Parser" class.  These are expected to be removed in
  future versions.

* Support for Pythons earlier than 2.3 has been removed.

Here are the differences between "email" version 2 and version 1:

* The "email.Header" and "email.Charset" modules have been added.

* The pickle format for "Message" instances has changed. Since this
  was never (and still isn’t) formally defined, this isn’t considered
  a backward incompatibility.  However if your application pickles and
  unpickles "Message" instances, be aware that in "email" version 2,
  "Message" instances now have private variables *_charset* and
  *_default_type*.

* Several methods in the "Message" class have been deprecated, or
  their signatures changed.  Also, many new methods have been added.
  See the documentation for the "Message" class for details.  The
  changes should be completely backward compatible.

* The object structure has changed in the face of *message/rfc822*
  content types.  In "email" version 1, such a type would be
  represented by a scalar payload, i.e. the container message’s
  "is_multipart()" returned false, "get_payload()" was not a list
  object, but a single "Message" instance.

  This structure was inconsistent with the rest of the package, so the
  object representation for *message/rfc822* content types was
  changed.  In "email" version 2, the container *does* return "True"
  from "is_multipart()", and "get_payload()" returns a list containing
  a single "Message" item.

  Note that this is one place that backward compatibility could not be
  completely maintained.  However, if you’re already testing the
  return type of "get_payload()", you should be fine.  You just need
  to make sure your code doesn’t do a "set_payload()" with a "Message"
  instance on a container with a content type of *message/rfc822*.

* The "Parser" constructor’s *strict* argument was added, and its
  "parse()" and "parsestr()" methods grew a *headersonly* argument.
  The *strict* flag was also added to functions
  "email.message_from_file()" and "email.message_from_string()".

* "Generator.__call__()" is deprecated; use "Generator.flatten"
  instead.  The "Generator" class has also grown the "clone()" method.

* The "DecodedGenerator" class in the "email.generator" module was
  added.

* The intermediate base classes "MIMENonMultipart" and
  "MIMEMultipart" have been added, and interposed in the class
  hierarchy for most of the other MIME-related derived classes.

* The *_encoder* argument to the "MIMEText" constructor has been
  deprecated.  Encoding  now happens implicitly based on the
  *_charset* argument.

* The following functions in the "email.Utils" module have been
  deprecated: "dump_address_pairs()", "decode()", and "encode()".  The
  following functions have been added to the module: "make_msgid()",
  "decode_rfc2231()", "encode_rfc2231()", and "decode_params()".

* The non-public function "email.Iterators._structure()" was added.


19.1.16. Differences from "mimelib"
===================================

The "email" package was originally prototyped as a separate library
called mimelib. Changes have been made so that method names are more
consistent, and some methods or modules have either been added or
removed.  The semantics of some of the methods have also changed.  For
the most part, any functionality available in "mimelib" is still
available in the "email" package, albeit often in a different way.
Backward compatibility between the "mimelib" package and the "email"
package was not a priority.

Here is a brief description of the differences between the "mimelib"
and the "email" packages, along with hints on how to port your
applications.

Of course, the most visible difference between the two packages is
that the package name has been changed to "email".  In addition, the
top-level package has the following differences:

* "messageFromString()" has been renamed to "message_from_string()".

* "messageFromFile()" has been renamed to "message_from_file()".

The "Message" class has the following differences:

* The method "asString()" was renamed to "as_string()".

* The method "ismultipart()" was renamed to "is_multipart()".

* The "get_payload()" method has grown a *decode* optional argument.

* The method "getall()" was renamed to "get_all()".

* The method "addheader()" was renamed to "add_header()".

* The method "gettype()" was renamed to "get_type()".

* The method "getmaintype()" was renamed to "get_main_type()".

* The method "getsubtype()" was renamed to "get_subtype()".

* The method "getparams()" was renamed to "get_params()". Also,
  whereas "getparams()" returned a list of strings, "get_params()"
  returns a list of 2-tuples, effectively the key/value pairs of the
  parameters, split on the "'='" sign.

* The method "getparam()" was renamed to "get_param()".

* The method "getcharsets()" was renamed to "get_charsets()".

* The method "getfilename()" was renamed to "get_filename()".

* The method "getboundary()" was renamed to "get_boundary()".

* The method "setboundary()" was renamed to "set_boundary()".

* The method "getdecodedpayload()" was removed.  To get similar
  functionality, pass the value 1 to the *decode* flag of the
  "get_payload()" method.

* The method "getpayloadastext()" was removed.  Similar
  functionality is supported by the "DecodedGenerator" class in the
  "email.generator" module.

* The method "getbodyastext()" was removed.  You can get similar
  functionality by creating an iterator with
  "typed_subpart_iterator()" in the "email.iterators" module.

The "Parser" class has no differences in its public interface. It does
have some additional smarts to recognize *message/delivery-status*
type messages, which it represents as a "Message" instance containing
separate "Message" subparts for each header block in the delivery
status notification [1].

The "Generator" class has no differences in its public interface.
There is a new class in the "email.generator" module though, called
"DecodedGenerator" which provides most of the functionality previously
available in the "Message.getpayloadastext()" method.

The following modules and classes have been changed:

* The "MIMEBase" class constructor arguments *_major* and *_minor*
  have changed to *_maintype* and *_subtype* respectively.

* The "Image" class/module has been renamed to "MIMEImage".  The
  *_minor* argument has been renamed to *_subtype*.

* The "Text" class/module has been renamed to "MIMEText".  The
  *_minor* argument has been renamed to *_subtype*.

* The "MessageRFC822" class/module has been renamed to
  "MIMEMessage". Note that an earlier version of "mimelib" called this
  class/module "RFC822", but that clashed with the Python standard
  library module "rfc822" on some case-insensitive file systems.

  Also, the "MIMEMessage" class now represents any kind of MIME
  message with main type *message*.  It takes an optional argument
  *_subtype* which is used to set the MIME subtype.  *_subtype*
  defaults to *rfc822*.

"mimelib" provided some utility functions in its "address" and "date"
modules.  All of these functions have been moved to the "email.utils"
module.

The "MsgReader" class/module has been removed.  Its functionality is
most closely supported in the "body_line_iterator()" function in the
"email.iterators" module.

-[ Footnotes ]-

[1] Delivery Status Notifications (DSN) are defined in **RFC
    1894**.
