# 18.1.8. `email.errors`: 异常和缺陷类

以下异常类在 `email.errors` 模块中定义：

exception `email.errors.``MessageError`

  这是 `email` 包可以引发的所有异常的基类。 它源自标准异常 `Exception` 类，这个类没有定义其他方法。

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`

  当使用 `add_payload()` 将有效负载添加到 `Message` 对象时，有效负载已经是一个标量，而消息的 Content-Type 主类型不是 multipart 或者缺少时触发该异常。 `MultipartConversionError` 多重继承自 `MessageError` 和内置的 `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!

2.4 新版功能: All the defect classes were added.

- `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.