# 12.5 `rfc822` -- Parse RFC 822 mail headers

This module defines a class, `Message`, which represents a collection of ``email headers'' as defined by the Internet standard RFC 822. It is used in various contexts, usually to read such headers from a file. This module also defines a helper class `AddressList` for parsing RFC 822 addresses.

Note that there's a separate module to read Unix, MH, and MMDF style mailbox files: `mailbox`.

`Message` (file[, seekable])
  A `Message` instance is instantiated with an input object as parameter. Message relies only on the input object having a `readline()` method; in particular, ordinary file objects qualify. Instantiation reads headers from the input object up to a delimiter line (normally a blank line) and stores them in the instance.

  This class can work with any input object that supports a `readline()` method. If the input object has seek and tell capability, the `rewindbody()` method will work; also, illegal lines will be pushed back onto the input stream. If the input object lacks seek but has an `unread()` method that can push back a line of input, `Message` will use that to push back illegal lines. Thus this class can be used to parse messages coming from a buffered stream.

  The optional seekable argument is provided as a workaround for certain stdio libraries in which `tell()` discards buffered data before discovering that the `lseek()` system call doesn't work. For maximum portability, you should set the seekable argument to zero to prevent that initial `tell()` when passing in an unseekable object such as a a file object created from a socket object.

  Input lines as read from the file may either be terminated by CR-LF or by a single linefeed; a terminating CR-LF is replaced by a single linefeed before the line is stored.

  All header matching is done independent of upper or lower case; e.g. `m['From']`, `m['from']` and `m['FROM']` all yield the same result.

`AddressList` (field)
  You may instantiate the AddresssList helper class using a single string parameter, a comma-separated list of RFC 822 addresses to be parsed. (The parameter `None` yields an empty list.)

`parsedate` (date)
  Attempts to parse a date according to the rules in RFC 822. however, some mailers don't follow that format as specified, so `parsedate()` tries to guess correctly in such cases. date is a string containing an RFC 822 date, such as `'Mon, 20 Nov 1995 19:12:08 -0500'`. If it succeeds in parsing the date, `parsedate()` returns a 9-tuple that can be passed directly to `time.mktime()`; otherwise `None` will be returned.

`parsedate_tz` (date)
  Performs the same function as `parsedate()`, but returns either `None` or a 10-tuple; the first 9 elements make up a tuple that can be passed directly to `time.mktime()`, and the tenth is the offset of the date's timezone from UTC (which is the official term for Greenwich Mean Time). (Note that the sign of the timezone offset is the opposite of the sign of the `time.timezone`variable for the same timezone; the latter variable follows the POSIX standard while this module follows RFC 822.) If the input string has no timezone, the last element of the tuple returned is `None`.

`mktime_tz` (tuple)
  Turn a 10-tuple as returned by `parsedate_tz()` into a UTC timestamp. It the timezone item in the tuple is `None`, assume local time. Minor deficiency: this first interprets the first 8 elements as a local time and then compensates for the timezone difference; this may yield a slight error around daylight savings time switch dates. Not enough to worry about for common use.

- 12.5.1 Message Objects
- 12.5.2 AddressList Objects