##
12.5.1 Message Objects

A `Message` instance has the following methods:

`rewindbody` ()
  Seek to the start of the message body. This only works if the file object is seekable.

`isheader` (line)
  Returns a line's canonicalized fieldname (the dictionary key that will be used to index it) if the line is a legal RFC822 header; otherwise returns None (implying that parsing should stop here and the line be pushed back on the input stream). It is sometimes useful to override this method in a subclass.

`islast` (line)
  Return true if the given line is a delimiter on which Message should stop. The delimiter line is consumed, and the file object's read location positioned immediately after it. By default this method just checks that the line is blank, but you can override it in a subclass.

`iscomment` (line)
  Return true if the given line should be ignored entirely, just skipped. By default this is a stub that always returns false, but you can override it in a subclass.

`getallmatchingheaders` (name)
  Return a list of lines consisting of all headers matching name, if any. Each physical line, whether it is a continuation line or not, is a separate list item. Return the empty list if no header matches name.

`getfirstmatchingheader` (name)
  Return a list of lines comprising the first header matching name, and its continuation line(s), if any. Return `None`if there is no header matching name.

`getrawheader` (name)
  Return a single string consisting of the text after the colon in the first header matching name. This includes leading whitespace, the trailing linefeed, and internal linefeeds and whitespace if there any continuation line(s) were present. Return `None` if there is no header matching name.

`getheader` (name[, default])
  Like `getrawheader(name)`, but strip leading and trailing whitespace. Internal whitespace is not stripped. The optional default argument can be used to specify a different default to be returned when there is no header matching name.

`get` (name[, default])
  An alias for `getheader()`, to make the interface more compatible with regular dictionaries.

`getaddr` (name)
  Return a pair `(full name, email address)` parsed from the string returned by `getheader(name)`. If no header matching name exists, return `(None, None)`; otherwise both the full name and the address are (possibly empty) strings.

  Example: If m's first `From` header contains the string `'jack@cwi.nl (Jack Jansen)'`, then `m.getaddr('From')` will yield the pair `('Jack Jansen', 'jack@cwi.nl')`. If the header contained `'Jack Jansen <jack@cwi.nl>'` instead, it would yield the exact same result.

`getaddrlist` (name)
  This is similar to `getaddr(list)`, but parses a header containing a list of email addresses (e.g. a `To` header) and returns a list of `(full name, email address)` pairs (even if there was only one address in the header). If there is no header matching name, return an empty list.

  If multiple headers exist that match the named header (e.g. if there are several `Cc` headers), all are parsed for addresses. Any continuation lines the named headers contain are also parsed.

  XXX The current version of this function is not really correct. It yields bogus results if a full name contains a comma.

`getdate` (name)
  Retrieve a header using `getheader()` and parse it into a 9-tuple compatible with `time.mktime()`. If there is no header matching name, or it is unparsable, return `None`.

  Date parsing appears to be a black art, and not all mailers adhere to the standard. While it has been tested and found correct on a large collection of email from many sources, it is still possible that this function may occasionally yield an incorrect result.

`getdate_tz` (name)
  Retrieve a header using `getheader()` and parse it into a 10-tuple; the first 9 elements will make a tuple compatible with `time.mktime()`, and the 10th is a number giving the offset of the date's timezone from UTC. Similarly to `getdate()`, if there is no header matching name, or it is unparsable, return `None`.

`Message` instances also support a read-only mapping interface. In particular: `m[name]` is like `m.getheader(name)` but raises `KeyError` if there is no matching header; and `len(m)`, `m.has_key(name)`, `m.keys()`, `m.values()` and `m.items()` act as expected (and consistently).

Finally, `Message` instances have two public instance variables:

`headers`
  A list containing the entire set of header lines, in the order in which they were read (except that setitem calls may disturb this order). Each line contains a trailing newline. The blank line terminating the headers is not contained in the list.

`fp`
  The file object passed at instantiation time.