"email.message": 電子メールメッセージの表現
*******************************************

The central class in the "email" package is the "Message" class,
imported from the "email.message" module.  It is the base class for
the "email" object model.  "Message" provides the core functionality
for setting and querying header fields, and for accessing message
bodies.

Conceptually, a "Message" object consists of *headers* and *payloads*.
Headers are **RFC 2822** style field names and values where the field
name and value are separated by a colon.  The colon is not part of
either the field name or the field value.

Headers are stored and returned in case-preserving form but are
matched case-insensitively.  There may also be a single envelope
header, also known as the *Unix-From* header or the "From_" header.
The payload is either a string in the case of simple message objects
or a list of "Message" objects for MIME container documents (e.g.
*multipart/** and *message/rfc822*).

"Message" objects provide a mapping style interface for accessing the
message headers, and an explicit interface for accessing both the
headers and the payload.  It provides convenience methods for
generating a flat text representation of the message object tree, for
accessing commonly used header parameters, and for recursively walking
over the object tree.

Here are the methods of the "Message" class:

class email.message.Message

   The constructor takes no arguments.

   as_string([unixfrom])

      Return the entire message flattened as a string.  When optional
      *unixfrom* is "True", the envelope header is included in the
      returned string. *unixfrom* defaults to "False".  Flattening the
      message may trigger changes to the "Message" if defaults need to
      be filled in to complete the transformation to a string (for
      example, MIME boundaries may be generated or modified).

      Note that this method is provided as a convenience and may not
      always format the message the way you want.  For example, by
      default it mangles lines that begin with "From".  For more
      flexibility, instantiate a "Generator" instance and use its
      "flatten()" method directly.  For example:

         from cStringIO import StringIO
         from email.generator import Generator
         fp = StringIO()
         g = Generator(fp, mangle_from_=False, maxheaderlen=60)
         g.flatten(msg)
         text = fp.getvalue()

   __str__()

      Equivalent to "as_string(unixfrom=True)".

   is_multipart()

      Return "True" if the message’s payload is a list of
      sub-"Message" objects, otherwise return "False".  When
      "is_multipart()" returns "False", the payload should be a string
      object.

   set_unixfrom(unixfrom)

      Set the message’s envelope header to *unixfrom*, which should be
      a string.

   get_unixfrom()

      メッセージのエンベロープヘッダを返します。エンベロープヘッダが設
      定されていない場合は "None" が返されます。

   attach(payload)

      Add the given *payload* to the current payload, which must be
      "None" or a list of "Message" objects before the call. After the
      call, the payload will always be a list of "Message" objects.
      If you want to set the payload to a scalar object (e.g. a
      string), use "set_payload()" instead.

   get_payload([i[, decode]])

      Return the current payload, which will be a list of "Message"
      objects when "is_multipart()" is "True", or a string when
      "is_multipart()" is "False".  If the payload is a list and you
      mutate the list object, you modify the message’s payload in
      place.

      With optional argument *i*, "get_payload()" will return the
      *i*-th element of the payload, counting from zero, if
      "is_multipart()" is "True".  An "IndexError" will be raised if
      *i* is less than 0 or greater than or equal to the number of
      items in the payload.  If the payload is a string (i.e.
      "is_multipart()" is "False") and *i* is given, a "TypeError" is
      raised.

      Optional *decode* is a flag indicating whether the payload
      should be decoded or not, according to the *Content-Transfer-
      Encoding* header. When "True" and the message is not a
      multipart, the payload will be decoded if this header’s value is
      "quoted-printable" or "base64". If some other encoding is used,
      or *Content-Transfer-Encoding* header is missing, or if the
      payload has bogus base64 data, the payload is returned as-is
      (undecoded).  If the message is a multipart and the *decode*
      flag is "True", then "None" is returned.  The default for
      *decode* is "False".

   set_payload(payload[, charset])

      Set the entire message object’s payload to *payload*.  It is the
      client’s responsibility to ensure the payload invariants.
      Optional *charset* sets the message’s default character set; see
      "set_charset()" for details.

      バージョン 2.2.2 で変更: *charset* argument added.

   set_charset(charset)

      Set the character set of the payload to *charset*, which can
      either be a "Charset" instance (see "email.charset"), a string
      naming a character set, or "None".  If it is a string, it will
      be converted to a "Charset" instance.  If *charset* is "None",
      the "charset" parameter will be removed from the *Content-Type*
      header (the message will not be otherwise modified).  Anything
      else will generate a "TypeError".

      If there is no existing *MIME-Version* header one will be added.
      If there is no existing *Content-Type* header, one will be added
      with a value of *text/plain*.  Whether the *Content-Type* header
      already exists or not, its "charset" parameter will be set to
      *charset.output_charset*.   If *charset.input_charset* and
      *charset.output_charset* differ, the payload will be re-encoded
      to the *output_charset*.  If there is no existing *Content-
      Transfer-Encoding* header, then the payload will be transfer-
      encoded, if needed, using the specified "Charset", and a header
      with the appropriate value will be added.  If a *Content-
      Transfer-Encoding* header already exists, the payload is assumed
      to already be correctly encoded using that *Content-Transfer-
      Encoding* and is not modified.

      The message will be assumed to be of type *text/**, with the
      payload either in unicode or encoded with
      *charset.input_charset*. It will be encoded or converted to
      *charset.output_charset* and transfer encoded properly, if
      needed, when generating the plain text representation of the
      message.  MIME headers (*MIME-Version*, *Content-Type*,
      *Content-Transfer-Encoding*) will be added as needed.

      バージョン 2.2.2 で追加.

   get_charset()

      Return the "Charset" instance associated with the message’s
      payload.

      バージョン 2.2.2 で追加.

   The following methods implement a mapping-like interface for
   accessing the message’s **RFC 2822** headers.  Note that there are
   some semantic differences between these methods and a normal
   mapping (i.e. dictionary) interface.  For example, in a dictionary
   there are no duplicate keys, but here there may be duplicate
   message headers.  Also, in dictionaries there is no guaranteed
   order to the keys returned by "keys()", but in a "Message" object,
   headers are always returned in the order they appeared in the
   original message, or were added to the message later.  Any header
   deleted and then re-added are always appended to the end of the
   header list.

   These semantic differences are intentional and are biased toward
   maximal convenience.

   注意: どんな場合も、メッセージ中のエンベロープヘッダはこのマップ形
   式のインタフェイスには含まれません。

   __len__()

      複製されたものもふくめてヘッダ数の合計を返します。

   __contains__(name)

      Return true if the message object has a field named *name*.
      Matching is done case-insensitively and *name* should not
      include the trailing colon. Used for the "in" operator, e.g.:

         if 'message-id' in myMessage:
             print 'Message-ID:', myMessage['message-id']

   __getitem__(name)

      Return the value of the named header field.  *name* should not
      include the colon field separator.  If the header is missing,
      "None" is returned; a "KeyError" is never raised.

      Note that if the named field appears more than once in the
      message’s headers, exactly which of those field values will be
      returned is undefined.  Use the "get_all()" method to get the
      values of all the extant named headers.

   __setitem__(name, val)

      Add a header to the message with field name *name* and value
      *val*.  The field is appended to the end of the message’s
      existing fields.

      注意: このメソッドでは、すでに同一の名前で存在するフィールドは上
      書き *されません*。もしメッセージが名前 *name* をもつフィールド
      をひとつしか持たないようにしたければ、最初にそれを除去してくださ
      い。たとえば:

         del msg['subject']
         msg['subject'] = 'Python roolz!'

   __delitem__(name)

      メッセージのヘッダから、*name* という名前をもつフィールドをすべ
      て除去します。たとえこの名前をもつヘッダが存在していなくても例外
      は発生しません。

   has_key(name)

      Return true if the message contains a header field named *name*,
      otherwise return false.

   keys()

      メッセージ中にあるすべてのヘッダのフィールド名のリストを返します
      。

   values()

      メッセージ中にあるすべてのフィールドの値のリストを返します。

   items()

      メッセージ中にあるすべてのヘッダのフィールド名とその値を 2-タプ
      ルのリストとして返します。

   get(name[, failobj])

      Return the value of the named header field.  This is identical
      to "__getitem__()" except that optional *failobj* is returned if
      the named header is missing (defaults to "None").

   Here are some additional useful methods:

   get_all(name[, failobj])

      *name* の名前をもつフィールドのすべての値からなるリストを返しま
      す。該当する名前のヘッダがメッセージ中に含まれていない場合は
      *failobj* (デフォルトでは "None") が返されます。

   add_header(_name, _value, **_params)

      拡張ヘッダ設定。このメソッドは "__setitem__()" と似ていますが、
      追加のヘッダ・パラメータをキーワード引数で指定できるところが違っ
      ています。 *_name* に追加するヘッダフィールドを、 *_value* にそ
      のヘッダの *最初の* 値を渡します。

      For each item in the keyword argument dictionary *_params*, the
      key is taken as the parameter name, with underscores converted
      to dashes (since dashes are illegal in Python identifiers).
      Normally, the parameter will be added as "key="value"" unless
      the value is "None", in which case only the key will be added.
      If the value contains non-ASCII characters, it must be specified
      as a three tuple in the format "(CHARSET, LANGUAGE, VALUE)",
      where "CHARSET" is a string naming the charset to be used to
      encode the value, "LANGUAGE" can usually be set to "None" or the
      empty string (see **RFC 2231** for other possibilities), and
      "VALUE" is the string value containing non-ASCII code points.

      Here’s an example:

         msg.add_header('Content-Disposition', 'attachment', filename='bud.gif')

      こうするとヘッダには以下のように追加されます

         Content-Disposition: attachment; filename="bud.gif"

      An example with non-ASCII characters:

         msg.add_header('Content-Disposition', 'attachment',
                        filename=('iso-8859-1', '', 'Fußballer.ppt'))

      Which produces

         Content-Disposition: attachment; filename*="iso-8859-1''Fu%DFballer.ppt"

   replace_header(_name, _value)

      Replace a header.  Replace the first header found in the message
      that matches *_name*, retaining header order and field name
      case.  If no matching header was found, a "KeyError" is raised.

      バージョン 2.2.2 で追加.

   get_content_type()

      Return the message’s content type.  The returned string is
      coerced to lower case of the form *maintype/subtype*.  If there
      was no *Content-Type* header in the message the default type as
      given by "get_default_type()" will be returned.  Since according
      to **RFC 2045**, messages always have a default type,
      "get_content_type()" will always return a value.

      **RFC 2045** defines a message’s default type to be *text/plain*
      unless it appears inside a *multipart/digest* container, in
      which case it would be *message/rfc822*.  If the *Content-Type*
      header has an invalid type specification, **RFC 2045** mandates
      that the default type be *text/plain*.

      バージョン 2.2.2 で追加.

   get_content_maintype()

      そのメッセージの主 content-type を返します。これは
      "get_content_type()" によって返される文字列の *maintype* 部分で
      す。

      バージョン 2.2.2 で追加.

   get_content_subtype()

      そのメッセージの副 content-type (sub content-type、subtype) を返
      します。これは "get_content_type()" によって返される文字列の
      *subtype* 部分です。

      バージョン 2.2.2 で追加.

   get_default_type()

      デフォルトの content-type を返します。ほどんどのメッセージではデ
      フォルトの content-type は *text/plain* ですが、メッセージが
      *multipart/digest* コンテナに含まれているときだけ例外的に
      *message/rfc822* になります。

      バージョン 2.2.2 で追加.

   set_default_type(ctype)

      Set the default content type.  *ctype* should either be
      *text/plain* or *message/rfc822*, although this is not enforced.
      The default content type is not stored in the *Content-Type*
      header.

      バージョン 2.2.2 で追加.

   get_params([failobj[, header[, unquote]]])

      Return the message’s *Content-Type* parameters, as a list. The
      elements of the returned list are 2-tuples of key/value pairs,
      as split on the "'='" sign.  The left hand side of the "'='" is
      the key, while the right hand side is the value.  If there is no
      "'='" sign in the parameter the value is the empty string,
      otherwise the value is as described in "get_param()" and is
      unquoted if optional *unquote* is "True" (the default).

      Optional *failobj* is the object to return if there is no
      *Content-Type* header.  Optional *header* is the header to
      search instead of *Content-Type*.

      バージョン 2.2.2 で変更: *unquote* argument added.

   get_param(param[, failobj[, header[, unquote]]])

      Return the value of the *Content-Type* header’s parameter
      *param* as a string.  If the message has no *Content-Type*
      header or if there is no such parameter, then *failobj* is
      returned (defaults to "None").

      Optional *header* if given, specifies the message header to use
      instead of *Content-Type*.

      Parameter keys are always compared case insensitively.  The
      return value can either be a string, or a 3-tuple if the
      parameter was **RFC 2231** encoded.  When it’s a 3-tuple, the
      elements of the value are of the form "(CHARSET, LANGUAGE,
      VALUE)".  Note that both "CHARSET" and "LANGUAGE" can be "None",
      in which case you should consider "VALUE" to be encoded in the
      "us-ascii" charset.  You can usually ignore "LANGUAGE".

      If your application doesn’t care whether the parameter was
      encoded as in **RFC 2231**, you can collapse the parameter value
      by calling "email.utils.collapse_rfc2231_value()", passing in
      the return value from "get_param()".  This will return a
      suitably decoded Unicode string when the value is a tuple, or
      the original string unquoted if it isn’t.  For example:

         rawparam = msg.get_param('foo')
         param = email.utils.collapse_rfc2231_value(rawparam)

      In any case, the parameter value (either the returned string, or
      the "VALUE" item in the 3-tuple) is always unquoted, unless
      *unquote* is set to "False".

      バージョン 2.2.2 で変更: *unquote* argument added, and 3-tuple
      return value possible.

   set_param(param, value[, header[, requote[, charset[, language]]]])

      Set a parameter in the *Content-Type* header.  If the parameter
      already exists in the header, its value will be replaced with
      *value*.  If the *Content-Type* header as not yet been defined
      for this message, it will be set to *text/plain* and the new
      parameter value will be appended as per **RFC 2045**.

      Optional *header* specifies an alternative header to *Content-
      Type*, and all parameters will be quoted as necessary unless
      optional *requote* is "False" (the default is "True").

      If optional *charset* is specified, the parameter will be
      encoded according to **RFC 2231**. Optional *language* specifies
      the RFC 2231 language, defaulting to the empty string.  Both
      *charset* and *language* should be strings.

      バージョン 2.2.2 で追加.

   del_param(param[, header[, requote]])

      Remove the given parameter completely from the *Content-Type*
      header.  The header will be re-written in place without the
      parameter or its value.  All values will be quoted as necessary
      unless *requote* is "False" (the default is "True").  Optional
      *header* specifies an alternative to *Content-Type*.

      バージョン 2.2.2 で追加.

   set_type(type[, header][, requote])

      Set the main type and subtype for the *Content-Type* header.
      *type* must be a string in the form *maintype/subtype*,
      otherwise a "ValueError" is raised.

      This method replaces the *Content-Type* header, keeping all the
      parameters in place.  If *requote* is "False", this leaves the
      existing header’s quoting as is, otherwise the parameters will
      be quoted (the default).

      An alternative header can be specified in the *header* argument.
      When the *Content-Type* header is set a *MIME-Version* header is
      also added.

      バージョン 2.2.2 で追加.

   get_filename([failobj])

      そのメッセージ中の *Content-Disposition* ヘッダにある、
      "filename" パラメータの値を返します。目的のヘッダに "filename"
      パラメータがない場合には *Content-Type* ヘッダにある "name" パラ
      メータを探します。それも無い場合またはヘッダが無い場合には
      *failobj* が返されます。返される文字列はつねに
      "email.utils.unquote()" によって unquote されます。

   get_boundary([failobj])

      そのメッセージ中の *Content-Type* ヘッダにある、 "boundary" パラ
      メータの値を返します。目的のヘッダが欠けていたり、 "boundary" パ
      ラメータがない場合には *failobj* が返されます。返される文字列は
      つねに "email.utils.unquote()" によって unquote されます。

   set_boundary(boundary)

      メッセージ中の *Content-Type* ヘッダにある、 "boundary" パラメー
      タに値を設定します。 "set_boundary()" は必要に応じて *boundary*
      を quote します。そのメッセージが *Content-Type* ヘッダを含んで
      いない場合、 "HeaderParseError" が発生します。

      Note that using this method is subtly different than deleting
      the old *Content-Type* header and adding a new one with the new
      boundary via "add_header()", because "set_boundary()" preserves
      the order of the *Content-Type* header in the list of headers.
      However, it does *not* preserve any continuation lines which may
      have been present in the original *Content-Type* header.

   get_content_charset([failobj])

      そのメッセージ中の *Content-Type* ヘッダにある、 "charset" パラ
      メータの値を返します。値はすべて小文字に変換されます。メッセージ
      中に *Content-Type* がなかったり、このヘッダ中に "charaset" パラ
      メータがない場合には *failobj* が返されます。

      Note that this method differs from "get_charset()" which returns
      the "Charset" instance for the default encoding of the message
      body.

      バージョン 2.2.2 で追加.

   get_charsets([failobj])

      メッセージ中に含まれる文字セットの名前をすべてリストにして返しま
      す。そのメッセージが *multipart* である場合、返されるリストの各
      要素がそれぞれの subpart のペイロードに対応します。それ以外の場
      合、これは長さ 1 のリストを返します。

      Each item in the list will be a string which is the value of the
      "charset" parameter in the *Content-Type* header for the
      represented subpart.  However, if the subpart has no *Content-
      Type* header, no "charset" parameter, or is not of the *text*
      main MIME type, then that item in the returned list will be
      *failobj*.

   walk()

      "walk()" メソッドは多目的のジェネレータで、これはあるメッセージ
      オブジェクトツリー中のすべての part および subpart をわたり歩く
      のに使えます。順序は深さ優先です。おそらく典型的な用法は、
      "walk()" を "for" ループ中でのイテレータとして使うことでしょう。
      ループを一回まわるごとに、次の subpart が返されるのです。

      Here’s an example that prints the MIME type of every part of a
      multipart message structure:

         >>> for part in msg.walk():
         ...     print part.get_content_type()
         multipart/report
         text/plain
         message/delivery-status
         text/plain
         text/plain
         message/rfc822

   バージョン 2.5 で変更: The previously deprecated methods
   "get_type()", "get_main_type()", and "get_subtype()" were removed.

   "Message" objects can also optionally contain two instance
   attributes, which can be used when generating the plain text of a
   MIME message.

   preamble

      MIME ドキュメントの形式では、ヘッダ直後にくる空行と最初の
      multipart 境界をあらわす文字列のあいだにいくらかのテキスト (訳注
      : preamble, 序文) を埋めこむことを許しています。このテキストは標
      準的な MIME の範疇からはみ出しているので、MIME 形式を認識するメ
      ールソフトからこれらは通常まったく見えません。しかしメッセージの
      テキストを生で見る場合、あるいはメッセージを MIME 対応していない
      メールソフトで見る場合、このテキストは目に見えることになります。

      *preamble* 属性は MIME ドキュメントに加えるこの最初の MIME 範囲
      外テキストを含んでいます。 "Parser" があるテキストをヘッダ以降に
      発見したが、それはまだ最初の MIME 境界文字列が現れる前だった場合
      、パーザはそのテキストをメッセージの *preamble* 属性に格納します
      。 "Generator" がある MIME メッセージからプレーンテキスト形式を
      生成するときメッセージが *preamble* 属性を持つことが発見されれば
      、これはそのテキストをヘッダと最初の MIME 境界の間に挿入します。
      詳細は "email.parser" および "email.generator" を参照してくださ
      い。

      注意: そのメッセージに preamble がない場合、*preamble* 属性には
      "None" が格納されます。

   epilogue

      The *epilogue* attribute acts the same way as the *preamble*
      attribute, except that it contains text that appears between the
      last boundary and the end of the message.

      バージョン 2.5 で変更: You do not need to set the epilogue to
      the empty string in order for the "Generator" to print a newline
      at the end of the file.

   defects

      *defects* 属性はメッセージを解析する途中で検出されたすべての問題
      点 (defect、障害) のリストを保持しています。解析中に発見されうる
      障害についてのより詳細な説明は "email.errors" を参照してください
      。

      バージョン 2.4 で追加.
