"email.mime"：從頭開始建立電子郵件和 MIME 物件
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**原始碼：**Lib/email/mime/

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This module is part of the legacy ("Compat32") email API.  Its
functionality is partially replaced by the "contentmanager" in the new
API, but in certain applications these classes may still be useful,
even in non-legacy code.

Ordinarily, you get a message object structure by passing a file or
some text to a parser, which parses the text and returns the root
message object.  However you can also build a complete message
structure from scratch, or even individual "Message" objects by hand.
In fact, you can also take an existing structure and add new "Message"
objects, move them around, etc.  This makes a very convenient
interface for slicing-and-dicing MIME messages.

You can create a new object structure by creating "Message" instances,
adding attachments and all the appropriate headers manually.  For MIME
messages though, the "email" package provides some convenient
subclasses to make things easier.

Here are the classes:

class email.mime.base.MIMEBase(_maintype, _subtype, *, policy=compat32, **_params)

   模組："email.mime.base"

   This is the base class for all the MIME-specific subclasses of
   "Message".  Ordinarily you won't create instances specifically of
   "MIMEBase", although you could.  "MIMEBase" is provided primarily
   as a convenient base class for more specific MIME-aware subclasses.

   *_maintype* is the *Content-Type* major type (e.g. *text* or
   *image*), and *_subtype* is the *Content-Type* minor type  (e.g.
   *plain* or *gif*).  *_params* is a parameter key/value dictionary
   and is passed directly to "Message.add_header".

   If *policy* is specified, (defaults to the "compat32" policy) it
   will be passed to "Message".

   The "MIMEBase" class always adds a *Content-Type* header (based on
   *_maintype*, *_subtype*, and *_params*), and a *MIME-Version*
   header (always set to "1.0").

   在 3.6 版的變更: 新增僅限關鍵字參數 *policy*。

class email.mime.nonmultipart.MIMENonMultipart

   模組："email.mime.nonmultipart"

   A subclass of "MIMEBase", this is an intermediate base class for
   MIME messages that are not *multipart*.  The primary purpose of
   this class is to prevent the use of the "attach()" method, which
   only makes sense for *multipart* messages.  If "attach()" is
   called, a "MultipartConversionError" exception is raised.

class email.mime.multipart.MIMEMultipart(_subtype='mixed', boundary=None, _subparts=None, *, policy=compat32, **_params)

   模組："email.mime.multipart"

   A subclass of "MIMEBase", this is an intermediate base class for
   MIME messages that are *multipart*.  Optional *_subtype* defaults
   to *mixed*, but can be used to specify the subtype of the message.
   A *Content-Type* header of *multipart/_subtype* will be added to
   the message object.  A *MIME-Version* header will also be added.

   Optional *boundary* is the multipart boundary string.  When "None"
   (the default), the boundary is calculated when needed (for example,
   when the message is serialized).

   *_subparts* is a sequence of initial subparts for the payload.  It
   must be possible to convert this sequence to a list.  You can
   always attach new subparts to the message by using the
   "Message.attach" method.

   Optional *policy* argument defaults to "compat32".

   Additional parameters for the *Content-Type* header are taken from
   the keyword arguments, or passed into the *_params* argument, which
   is a keyword dictionary.

   在 3.6 版的變更: 新增僅限關鍵字參數 *policy*。

class email.mime.application.MIMEApplication(_data, _subtype='octet-stream', _encoder=email.encoders.encode_base64, *, policy=compat32, **_params)

   模組："email.mime.application"

   A subclass of "MIMENonMultipart", the "MIMEApplication" class is
   used to represent MIME message objects of major type *application*.
   *_data* contains the bytes for the raw application data.  Optional
   *_subtype* specifies the MIME subtype and defaults to *octet-
   stream*.

   Optional *_encoder* is a callable (i.e. function) which will
   perform the actual encoding of the data for transport.  This
   callable takes one argument, which is the "MIMEApplication"
   instance. It should use "get_payload()" and "set_payload()" to
   change the payload to encoded form.  It should also add any
   *Content-Transfer-Encoding* or other headers to the message object
   as necessary.  The default encoding is base64.  See the
   "email.encoders" module for a list of the built-in encoders.

   Optional *policy* argument defaults to "compat32".

   *_params* are passed straight through to the base class
   constructor.

   在 3.6 版的變更: 新增僅限關鍵字參數 *policy*。

class email.mime.audio.MIMEAudio(_audiodata, _subtype=None, _encoder=email.encoders.encode_base64, *, policy=compat32, **_params)

   模組："email.mime.audio"

   A subclass of "MIMENonMultipart", the "MIMEAudio" class is used to
   create MIME message objects of major type *audio*. *_audiodata*
   contains the bytes for the raw audio data.  If this data can be
   decoded as au, wav, aiff, or aifc, then the subtype will be
   automatically included in the *Content-Type* header. Otherwise you
   can explicitly specify the audio subtype via the *_subtype*
   argument.  If the minor type could not be guessed and *_subtype*
   was not given, then "TypeError" is raised.

   Optional *_encoder* is a callable (i.e. function) which will
   perform the actual encoding of the audio data for transport.  This
   callable takes one argument, which is the "MIMEAudio" instance. It
   should use "get_payload()" and "set_payload()" to change the
   payload to encoded form.  It should also add any *Content-Transfer-
   Encoding* or other headers to the message object as necessary.  The
   default encoding is base64.  See the "email.encoders" module for a
   list of the built-in encoders.

   Optional *policy* argument defaults to "compat32".

   *_params* are passed straight through to the base class
   constructor.

   在 3.6 版的變更: 新增僅限關鍵字參數 *policy*。

class email.mime.image.MIMEImage(_imagedata, _subtype=None, _encoder=email.encoders.encode_base64, *, policy=compat32, **_params)

   模組："email.mime.image"

   A subclass of "MIMENonMultipart", the "MIMEImage" class is used to
   create MIME message objects of major type *image*. *_imagedata*
   contains the bytes for the raw image data.  If this data type can
   be detected (jpeg, png, gif, tiff, rgb, pbm, pgm, ppm, rast, xbm,
   bmp, webp, and exr attempted), then the subtype will be
   automatically included in the *Content-Type* header. Otherwise you
   can explicitly specify the image subtype via the *_subtype*
   argument. If the minor type could not be guessed and *_subtype* was
   not given, then "TypeError" is raised.

   Optional *_encoder* is a callable (i.e. function) which will
   perform the actual encoding of the image data for transport.  This
   callable takes one argument, which is the "MIMEImage" instance. It
   should use "get_payload()" and "set_payload()" to change the
   payload to encoded form.  It should also add any *Content-Transfer-
   Encoding* or other headers to the message object as necessary.  The
   default encoding is base64.  See the "email.encoders" module for a
   list of the built-in encoders.

   Optional *policy* argument defaults to "compat32".

   *_params* are passed straight through to the "MIMEBase"
   constructor.

   在 3.6 版的變更: 新增僅限關鍵字參數 *policy*。

class email.mime.message.MIMEMessage(_msg, _subtype='rfc822', *, policy=compat32)

   模組："email.mime.message"

   A subclass of "MIMENonMultipart", the "MIMEMessage" class is used
   to create MIME objects of main type *message*. *_msg* is used as
   the payload, and must be an instance of class "Message" (or a
   subclass thereof), otherwise a "TypeError" is raised.

   Optional *_subtype* sets the subtype of the message; it defaults to
   *rfc822*.

   Optional *policy* argument defaults to "compat32".

   在 3.6 版的變更: 新增僅限關鍵字參數 *policy*。

class email.mime.text.MIMEText(_text, _subtype='plain', _charset=None, *, policy=compat32)

   模組："email.mime.text"

   A subclass of "MIMENonMultipart", the "MIMEText" class is used to
   create MIME objects of major type *text*. *_text* is the string for
   the payload.  *_subtype* is the minor type and defaults to *plain*.
   *_charset* is the character set of the text and is passed as an
   argument to the "MIMENonMultipart" constructor; it defaults to "us-
   ascii" if the string contains only "ascii" code points, and "utf-8"
   otherwise.  The *_charset* parameter accepts either a string or a
   "Charset" instance.

   Unless the *_charset* argument is explicitly set to "None", the
   MIMEText object created will have both a *Content-Type* header with
   a "charset" parameter, and a *Content-Transfer-Encoding* header.
   This means that a subsequent "set_payload" call will not result in
   an encoded payload, even if a charset is passed in the
   "set_payload" command.  You can "reset" this behavior by deleting
   the "Content-Transfer-Encoding" header, after which a "set_payload"
   call will automatically encode the new payload (and add a new
   *Content-Transfer-Encoding* header).

   Optional *policy* argument defaults to "compat32".

   在 3.5 版的變更: *_charset* also accepts "Charset" instances.

   在 3.6 版的變更: 新增僅限關鍵字參數 *policy*。
