19.1.5. "email.errors": Exception and Defect classes
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**Source code:** Lib/email/errors.py

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The following exception classes are defined in the "email.errors"
module:

exception email.errors.MessageError

   This is the base class for all exceptions that the "email" package
   can raise.  It is derived from the standard "Exception" class and
   defines no additional methods.

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").

Here is the list of the defects that the "FeedParser" can find while
parsing messages.  Note that the defects are added to the message
where the problem was found, so for example, if a message nested
inside a *multipart/alternative* had a malformed header, that nested
message object would have a defect, but the containing messages would
not.

All defect classes are subclassed from "email.errors.MessageDefect".

* "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.

  New in version 3.3.

* "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.

  New in version 3.3.

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

  Deprecated since version 3.3: This defect has not been used for
  several Python versions.

* "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.
