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# 18.1.8. `email`: Exception and Defect classes

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`.

exception `email.errors.``HeaderParseError`

  Raised under some error conditions when parsing the RFC 2822 headers of a message, this class is derived from `MessageParseError`. It can be raised from the `Parser.parse()` or `Parser.parsestr()` methods.

  Situations where it can be raised include finding an envelope header after the first RFC 2822 header of the message, finding a continuation line before the first RFC 2822 header is found, or finding a line in the headers which is neither a header or a continuation line.

exception `email.errors.``BoundaryError`

  Raised under some error conditions when parsing the RFC 2822 headers of a message, this class is derived from `MessageParseError`. It can be raised from the `Parser.parse()` or `Parser.parsestr()` methods.

  Situations where it can be raised include not being able to find the starting or terminating boundary in a multipart/* message when strict parsing is 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’s 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`, but this class is not an exception!

- `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.
- `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.
- `MalformedHeaderDefect` – A header was found that was missing a colon, or was otherwise malformed.
- `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.

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