## 12.2.10 Iterators

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.

`body_line_iterator`(msg)
  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.

`typed_subpart_iterator`(msg[, maintype[, subtype]])
  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.

`_structure`(msg[, fp[, level]])
  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 extended print statement. level is used internally.