"email.errors": Exception and Defect classes
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**ソースコード:** Lib/email/errors.py

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"email.errors" モジュールでは、以下の例外クラスが定義されています:

exception email.errors.MessageError

   これは "email" パッケージが送出しうるすべての例外の基底クラスです。
   これは標準の "Exception" クラスから派生しており、追加のメソッドは定
   義されていません。

exception email.errors.MessageParseError

   This is the base class for exceptions raised by the "Parser" class.
   It is derived from "MessageError".  This class is also used
   internally by the parser used by "headerregistry".

exception email.errors.HeaderParseError

   Raised under some error conditions when parsing the **RFC 5322**
   headers of a message, this class is derived from
   "MessageParseError".  The "set_boundary()" method will raise this
   error if the content type is unknown when the method is called.
   "Header" may raise this error for certain base64 decoding errors,
   and when an attempt is made to create a header that appears to
   contain an embedded header (that is, there is what is supposed to
   be a continuation line that has no leading whitespace and looks
   like a header).

exception email.errors.BoundaryError

   Deprecated and no longer used.

exception email.errors.MultipartConversionError

   Raised when a payload is added to a "Message" object using
   "add_payload()", but the payload is already a scalar and the
   message's *Content-Type* main type is not either *multipart* or
   missing.  "MultipartConversionError" multiply inherits from
   "MessageError" and the built-in "TypeError".

   Since "Message.add_payload()" is deprecated, this exception is
   rarely raised in practice.  However the exception may also be
   raised if the "attach()" method is called on an instance of a class
   derived from "MIMENonMultipart" (e.g. "MIMEImage").

exception email.errors.HeaderWriteError

   Raised when an error occurs when the "generator" outputs headers.

exception email.errors.MessageDefect

   This is the base class for all defects found when parsing email
   messages. It is derived from "ValueError".

exception email.errors.HeaderDefect

   This is the base class for all defects found when parsing email
   headers. It is derived from "MessageDefect".

以下は "FeedParser" がメッセージの解析中に検出する障害 (defect) の一覧
です。これらの障害は、問題が見つかったメッセージに追加されるため、たと
えば *multipart/alternative* 内にあるネストしたメッセージが異常なヘッ
ダをもっていた場合には、そのネストしたメッセージが障害を持っているが、
その親メッセージには障害はないとみなされることに注意してください。

すべての障害クラスは "email.errors.MessageDefect" のサブクラスです。

* "NoBoundaryInMultipartDefect" -- A message claimed to be a
  multipart, but had no *boundary* parameter.

* "StartBoundaryNotFoundDefect" -- The start boundary claimed in the
  *Content-Type* header was never found.

* "CloseBoundaryNotFoundDefect" -- A start boundary was found, but no
  corresponding close boundary was ever found.

  バージョン 3.3 で追加.

* "FirstHeaderLineIsContinuationDefect" -- The message had a
  continuation line as its first header line.

* "MisplacedEnvelopeHeaderDefect" - A "Unix From" header was found in
  the middle of a header block.

* "MissingHeaderBodySeparatorDefect" - A line was found while parsing
  headers that had no leading white space but contained no ':'.
  Parsing continues assuming that the line represents the first line
  of the body.

  バージョン 3.3 で追加.

* "MalformedHeaderDefect" -- A header was found that was missing a
  colon, or was otherwise malformed.

  バージョン 3.3 で非推奨: この欠陥が使われていないPythonバージョンが
  いくつかあります。

* "MultipartInvariantViolationDefect" -- A message claimed to be a
  *multipart*, but no subparts were found.  Note that when a message
  has this defect, its "is_multipart()" method may return "False" even
  though its content type claims to be *multipart*.

* "InvalidBase64PaddingDefect" -- When decoding a block of base64
  encoded bytes, the padding was not correct.  Enough padding is added
  to perform the decode, but the resulting decoded bytes may be
  invalid.

* "InvalidBase64CharactersDefect" -- When decoding a block of base64
  encoded bytes, characters outside the base64 alphabet were
  encountered. The characters are ignored, but the resulting decoded
  bytes may be invalid.

* "InvalidBase64LengthDefect" -- When decoding a block of base64
  encoded bytes, the number of non-padding base64 characters was
  invalid (1 more than a multiple of 4).  The encoded block was kept
  as-is.

* "InvalidDateDefect" -- When decoding an invalid or unparsable date
  field. The original value is kept as-is.
