# `email.iterators`：疊代器

原始碼：Lib/email/iterators.py

Iterating over a message object tree is fairly easy with the `Message.walk` method. The `email.iterators` module provides some useful higher level iterations over message object trees.

email.iterators.body_line_iterator(msg, decode=False)

  This iterates over all the payloads in all the subparts of msg, returning the string payloads line-by-line. It skips over all the subpart headers, and it skips over any subpart with a payload that isn't a Python string. This is somewhat equivalent to reading the flat text representation of the message from a file using `readline()`, skipping over all the intervening headers.

  Optional decode is passed through to `Message.get_payload`.

email.iterators.typed_subpart_iterator(msg, maintype='text', subtype=None)

  This iterates over all the subparts of msg, returning only those subparts that match the MIME type specified by maintype and subtype.

  Note that subtype is optional; if omitted, then subpart MIME type matching is done only with the main type. maintype is optional too; it defaults to text.

  Thus, by default `typed_subpart_iterator()` returns each subpart that has a MIME type of text/*.

The following function has been added as a useful debugging tool. It should not be considered part of the supported public interface for the package.

email.iterators._structure(msg, fp=None, level=0, include_default=False)

  Prints an indented representation of the content types of the message object structure. For example:

      >>> msg = email.message_from_file(somefile)
      >>> _structure(msg)
      multipart/mixed
          text/plain
          text/plain
          multipart/digest
              message/rfc822
                  text/plain
              message/rfc822
                  text/plain
              message/rfc822
                  text/plain
              message/rfc822
                  text/plain
              message/rfc822
                  text/plain
          text/plain

  Optional fp is a file-like object to print the output to. It must be suitable for Python's `print()` function. level is used internally. include_default, if true, prints the default type as well.