# `email.message`: Representing an email message

ソースコード: Lib/email/message.py

Added in version 3.6: [1]

The central class in the `email` package is the `EmailMessage` class, imported from the `email.message` module. It is the base class for the `email` object model. `EmailMessage` provides the core functionality for setting and querying header fields, for accessing message bodies, and for creating or modifying structured messages.

An email message consists of headers and a payload (which is also referred to as the content). Headers are RFC 5322 or RFC 6532 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. The payload may be a simple text message, or a binary object, or a structured sequence of sub-messages each with their own set of headers and their own payload. The latter type of payload is indicated by the message having a MIME type such as multipart/* or message/rfc822.

The conceptual model provided by an `EmailMessage` object is that of an ordered dictionary of headers coupled with a payload that represents the RFC 5322 body of the message, which might be a list of sub-`EmailMessage` objects. In addition to the normal dictionary methods for accessing the header names and values, there are methods for accessing specialized information from the headers (for example the MIME content type), for operating on the payload, for generating a serialized version of the message, and for recursively walking over the object tree.

The `EmailMessage` dictionary-like interface is indexed by the header names, which must be ASCII values. The values of the dictionary are strings with some extra methods. Headers are stored and returned in case-preserving form, but field names are matched case-insensitively. The keys are ordered, but unlike a real dict, there can be duplicates. Additional methods are provided for working with headers that have duplicate keys.

The payload is either a string or bytes object, in the case of simple message objects, or a list of `EmailMessage` objects, for MIME container documents such as multipart/* and message/rfc822 message objects.

class email.message.EmailMessage(policy=default)

  If policy is specified use the rules it specifies to update 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.

  as_string(unixfrom=False, maxheaderlen=None, policy=None)

    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`. For backward compatibility with the base `Message` class maxheaderlen is accepted, but defaults to `None`, which means that by default the line length is controlled by the `max_line_length` of the policy. The policy argument may be used to override the default policy obtained from the message instance. This can be used to control some of the formatting produced by the method, since the specified policy will be passed to the `Generator`.

    もし、文字列への変換を完全に行うためにデフォルト値を埋める必要がある場合、メッセージのフラット化は `EmailMessage` の変更を引き起こす可能性があります (例えば、MIME の境界が生成される、変更される等)。

    Note that this method is provided as a convenience and may not be the most useful way to serialize messages in your application, especially if you are dealing with multiple messages. See `email.generator.Generator` for a more flexible API for serializing messages. Note also that this method is restricted to producing messages serialized as "7 bit clean" when `utf8` is `False`, which is the default.

    バージョン 3.6 で変更: the default behavior when maxheaderlen is not specified was changed from defaulting to 0 to defaulting to the value of max_line_length from the policy.

  __str__()

    Equivalent to `as_string(policy=self.policy.clone(utf8=True))`. Allows `str(msg)` to produce a string containing the serialized message in a readable format.

    バージョン 3.4 で変更: the method was changed to use `utf8=True`, thus producing an RFC 6531-like message representation, instead of being a direct alias for `as_string()`.

  as_bytes(unixfrom=False, policy=None)

    Return the entire message flattened as a bytes object. When optional unixfrom is true, the envelope header is included in the returned string. unixfrom defaults to `False`. The policy argument may be used to override the default policy obtained from the message instance. This can be used to control some of the formatting produced by the method, since the specified policy will be passed to the `BytesGenerator`.

    もし、文字列への変換を完全に行うためにデフォルト値を埋める必要がある場合、メッセージのフラット化は `EmailMessage` の変更を引き起こす可能性があります (例えば、MIME の境界が生成される、変更される等)。

    Note that this method is provided as a convenience and may not be the most useful way to serialize messages in your application, especially if you are dealing with multiple messages. See `email.generator.BytesGenerator` for a more flexible API for serializing messages.

  __bytes__()

    Equivalent to `as_bytes()`. Allows `bytes(msg)` to produce a bytes object containing the serialized message.

  is_multipart()

    Return `True` if the message's payload is a list of sub-`EmailMessage` objects, otherwise return `False`. When `is_multipart()` returns `False`, the payload should be a string object (which might be a CTE encoded binary payload). Note that `is_multipart()` returning `True` does not necessarily mean that "msg.get_content_maintype() == 'multipart'" will return the `True`. For example, `is_multipart` will return `True` when the `EmailMessage` is of type `message/rfc822`.

  set_unixfrom(unixfrom)

    Set the message's envelope header to unixfrom, which should be a string. (See `mboxMessage` for a brief description of this header.)

  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。

  The following methods implement the mapping-like interface for accessing the message's 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 an `EmailMessage` object, headers are always returned in the order they appeared in the original message, or in which they were added to the message later. Any header deleted and then re-added is always appended to the end of the header list.

  These semantic differences are intentional and are biased toward convenience in the most common use cases.

  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 without regard to case and name does not include the trailing colon. Used for the `in` operator. For example:

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

  __getitem__(name)

    Return the value of the named header field. name does 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 headers named name.

    Using the standard (non-`compat32`) policies, the returned value is an instance of a subclass of `email.headerregistry.BaseHeader`.

  __setitem__(name, val)

    メッセージヘッダに name という名前の val という値をもつフィールドをあらたに追加します。このフィールドは現在メッセージに存在するヘッダーのいちばん後に追加されます。

    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!'

    If the `policy` defines certain headers to be unique (as the standard policies do), this method may raise a `ValueError` when an attempt is made to assign a value to such a header when one already exists. This behavior is intentional for consistency's sake, but do not depend on it as we may choose to make such assignments do an automatic deletion of the existing header in the future.

  __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。

  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=None)

    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 (failobj defaults to `None`).

  Here are some additional useful header related methods:

  get_all(name, failobj=None)

    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, the charset and language may be explicitly controlled by specifying the value 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. If a three tuple is not passed and the value contains non-ASCII characters, it is automatically encoded in RFC 2231 format using a `CHARSET` of `utf-8` and a `LANGUAGE` of `None`.

    以下に例を示します。:

        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 of the extended interface with non-ASCII characters:

        msg.add_header('Content-Disposition', 'attachment',
                       filename=('iso-8859-1', '', 'Fußballer.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 of the original header. If no matching header is found, raise a `KeyError`.

  get_content_type()

    Return the message's content type, coerced to lower case of the form maintype/subtype. If there is no Content-Type header in the message return the value returned by `get_default_type()`. If the Content-Type header is invalid, return `text/plain`.

    (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.)

  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。

  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。

  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。

  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, so it only affects the return value of the `get_content_type` methods when no Content-Type header is present in the message.

  set_param(param, value, header='Content-Type', requote=True, charset=None, language='', replace=False)

    Set a parameter in the Content-Type header. If the parameter already exists in the header, replace its value with value. When header is `Content-Type` (the default) and the header does not yet exist in the message, add it, set its value to text/plain, and append the new parameter value. Optional header specifies an alternative header to Content-Type.

    If the value contains non-ASCII characters, the charset and language may be explicitly specified using the optional charset and language parameters. Optional language specifies the RFC 2231 language, defaulting to the empty string. Both charset and language should be strings. The default is to use the `utf8` charset and `None` for the language.

    If replace is `False` (the default) the header is moved to the end of the list of headers. If replace is `True`, the header will be updated in place.

    Use of the requote parameter with `EmailMessage` objects is deprecated.

    Note that existing parameter values of headers may be accessed through the `params` attribute of the header value (for example, `msg['Content-Type'].params['charset']`).

    バージョン 3.4 で変更: `replace` キーワードが追加されました。

  del_param(param, header='content-type', requote=True)

    指定されたパラメータを Content-Type ヘッダ中から完全にとりのぞきます。ヘッダはそのパラメータと値がない状態に書き換えられます。オプション変数 header が与えられた場合、 Content-Type のかわりにそのヘッダが使用されます。

    Use of the requote parameter with `EmailMessage` objects is deprecated.

  get_filename(failobj=None)

    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=None)

    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 from 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.

  get_content_charset(failobj=None)

    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。

  get_charsets(failobj=None)

    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。

    リスト中の各要素は文字列であり、これは対応する subpart 中のそれぞれの Content-Type ヘッダにある `charset` の値です。その subpart が Content-Type をもってないか、 `charset` がないか、あるいは MIME maintype が text でないいずれかの場合には、リストの要素として failobj が返されます。

  is_attachment()

    Content-Disposition ヘッダが存在し、その (大文字小文字を区別しない) 値が `attachment` の場合、 `True` を返します。 それ以外の場合は `False` を返します。

    バージョン 3.4.2 で変更: `is_multipart()` との一貫性のために、is_attachment が属性からメソッドになりました。

  get_content_disposition()

    Return the lowercased value (without parameters) of the message's Content-Disposition header if it has one, or `None`. The possible values for this method are inline, attachment or `None` if the message follows RFC 2183.

    Added in version 3.5.

  The following methods relate to interrogating and manipulating the content (payload) of the message.

  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。

    以下の例は、 multipart メッセージのすべての part において、その MIME タイプを表示していくものです。 :

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

    `walk` iterates over the subparts of any part where `is_multipart()` returns `True`, even though `msg.get_content_maintype() == 'multipart'` may return `False`. We can see this in our example by making use of the `_structure` debug helper function:

        >>> from email.iterators import _structure
        >>> for part in msg.walk():
        ...     print(part.get_content_maintype() == 'multipart',
        ...           part.is_multipart())
        True True
        False False
        False True
        False False
        False False
        False True
        False False
        >>> _structure(msg)
        multipart/report
            text/plain
            message/delivery-status
                text/plain
                text/plain
            message/rfc822
                text/plain

    Here the `message` parts are not `multiparts`, but they do contain subparts. `is_multipart()` returns `True` and `walk` descends into the subparts.

  get_body(preferencelist=('related', 'html', 'plain'))

    メッセージの "本体" の最有力候補となる MIME 部を返します。

    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 preferencelist, 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 immediate sub-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()

    ペイロードとヘッダの全てを削除します。

  clear_content()

    Remove the payload and all of the !Content- headers, leaving all other headers intact and in their original order.

  `EmailMessage` オブジェクトは次のようなインスタンス属性を持ちます:

  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. As with the `preamble`, if there is no epilog text this attribute will be `None`.

  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。

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.

脚注

[1]

Originally added in 3.4 as a provisional module. Docs for legacy message class moved to email.message.Message: compat32 API を使用した電子メールメッセージの表現.