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.