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# 18.1. `email` — 电子邮件与 MIME 处理包

2.2 新版功能.

The `email` package is a library for managing email messages, including MIME and other RFC 2822-based message documents. It subsumes most of the functionality in several older standard modules such as `rfc822`, `mimetools`, `multifile`, and other non-standard packages such as `mimecntl`. 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:

- 18.1.1. `email.message`: Representing an email message
- 18.1.2. `email.parser`: Parsing email messages
  - 18.1.2.1. FeedParser API
  - 18.1.2.2. Parser class API
  - 18.1.2.3. Additional notes
- 18.1.3. `email.generator`: Generating MIME documents
- 18.1.4. `email.mime`: Creating email and MIME objects from scratch
- 18.1.5. `email.header`: Internationalized headers
- 18.1.6. `email.charset`: Representing character sets
- 18.1.7. `email.encoders`: 编码器
- 18.1.8. `email.errors`: 异常和缺陷类
- 18.1.9. `email.utils`: 其他工具
- 18.1.10. `email.iterators`: 迭代器
- 18.1.11. `email`: Examples

参见

Module `smtplib`

  SMTP protocol client

Module `nntplib`

  NNTP protocol client

## 18.1.12. 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 | Python 2.3 to 2.5
`4.0` | Python 2.5 | Python 2.3 to 2.5

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.

## 18.1.13. 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.