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# 18.11. `rfc822` — Parse RFC 2822 mail headers

Deprecated since version 2.3: The `email` package should be used in preference to the `rfc822` module. This module is present only to maintain backward compatibility, and has been removed in Python 3.

This module defines a class, `Message`, which represents an “email message” as defined by the Internet standard RFC 2822. [1] Such messages consist of a collection of message headers, and a message body. This module also defines a helper class `AddressList` for parsing RFC 2822 addresses. Please refer to the RFC for information on the specific syntax of RFC 2822 messages.

The `mailbox` module provides classes to read mailboxes produced by various end-user mail programs.

class `rfc822.``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. The message body, following the headers, is not consumed.

  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 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.

class `rfc822.``AddressList`(field)

  You may instantiate the `AddressList` helper class using a single string parameter, a comma-separated list of RFC 2822 addresses to be parsed. (The parameter `None` yields an empty list.)

`rfc822.``quote`(str)

  Return a new string with backslashes in str replaced by two backslashes and double quotes replaced by backslash-double quote.

`rfc822.``unquote`(str)

  Return a new string which is an unquoted version of str. If str ends and begins with double quotes, they are stripped off. Likewise if str ends and begins with angle brackets, they are stripped off.

`rfc822.``parseaddr`(address)

  Parse address, which should be the value of some address-containing field such as To or Cc, into its constituent “realname” and “email address” parts. Returns a tuple of that information, unless the parse fails, in which case a 2-tuple `(None, None)` is returned.

`rfc822.``dump_address_pair`(pair)

  The inverse of `parseaddr()`, this takes a 2-tuple of the form `(realname, email_address)` and returns the string value suitable for a To or Cc header. If the first element of pair is false, then the second element is returned unmodified.

`rfc822.``parsedate`(date)

  Attempts to parse a date according to the rules in RFC 2822. 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 2822 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. Note that indexes 6, 7, and 8 of the result tuple are not usable.

`rfc822.``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 2822.) If the input string has no timezone, the last element of the tuple returned is `None`. Note that indexes 6, 7, and 8 of the result tuple are not usable.

`rfc822.``mktime_tz`(tuple)

  Turn a 10-tuple as returned by `parsedate_tz()` into a UTC timestamp. If 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.

See also

Module `email`
  Comprehensive email handling package; supersedes the `rfc822` module.
Module `mailbox`
  Classes to read various mailbox formats produced by end-user mail programs.
Module `mimetools`
  Subclass of `rfc822.Message` that handles MIME encoded messages.

## 18.11.1. Message Objects

A `Message` instance has the following methods:

`Message.``rewindbody`()

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

`Message.``isheader`(line)

  Returns a line’s canonicalized fieldname (the dictionary key that will be used to index it) if the line is a legal RFC 2822 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.

`Message.``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.

`Message.``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.

`Message.``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.

`Message.``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.

`Message.``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.

`Message.``getheader`(name[, default])

  Return a single string consisting of the last header matching 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; it defaults to `None`. This is the preferred way to get parsed headers.

`Message.``get`(name[, default])

  An alias for `getheader()`, to make the interface more compatible with regular dictionaries.

`Message.``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.

`Message.``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.

`Message.``getdate`(name)

  Retrieve a header using `getheader()` and parse it into a 9-tuple compatible with `time.mktime()`; note that fields 6, 7, and 8 are not usable. 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.

`Message.``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. Note that fields 6, 7, and 8 are not usable. Similarly to `getdate()`, if there is no header matching name, or it is unparsable, return `None`.

`Message` instances also support a limited mapping interface. In particular: `m[name]` is like `m.getheader(name)` but raises `KeyError` if there is no matching header; and `len(m)`, `m.get(name[, default])`, `name in m`, `m.keys()`, `m.values()` `m.items()`, and `m.setdefault(name[, default])` act as expected, with the one difference that `setdefault()` uses an empty string as the default value. `Message` instances also support the mapping writable interface `m[name] = value` and `del m[name]`. `Message` objects do not support the `clear()`, `copy()`, `popitem()`, or `update()` methods of the mapping interface. (Support for `get()` and `setdefault()` was only added in Python 2.2.)

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

`Message.``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.

`Message.``fp`

  The file or file-like object passed at instantiation time. This can be used to read the message content.

`Message.``unixfrom`

  The Unix `From` line, if the message had one, or an empty string. This is needed to regenerate the message in some contexts, such as an `mbox`-style mailbox file.

## 18.11.2. AddressList Objects

An `AddressList` instance has the following methods:

`AddressList.``__len__`()

  Return the number of addresses in the address list.

`AddressList.``__str__`()

  Return a canonicalized string representation of the address list. Addresses are rendered in “name” <host@domain> form, comma-separated.

`AddressList.``__add__`(alist)

  Return a new `AddressList` instance that contains all addresses in both `AddressList` operands, with duplicates removed (set union).

`AddressList.``__iadd__`(alist)

  In-place version of `__add__()`; turns this `AddressList` instance into the union of itself and the right-hand instance, alist.

`AddressList.``__sub__`(alist)

  Return a new `AddressList` instance that contains every address in the left-hand `AddressList` operand that is not present in the right-hand address operand (set difference).

`AddressList.``__isub__`(alist)

  In-place version of `__sub__()`, removing addresses in this list which are also in alist.

Finally, `AddressList` instances have one public instance variable:

`AddressList.``addresslist`

  A list of tuple string pairs, one per address. In each member, the first is the canonicalized name part, the second is the actual route-address (`'@'`-separated username-host.domain pair).

Footnotes

[1] | This module originally conformed to RFC 822, hence the name. Since then, RFC 2822 has been released as an update to RFC 822. This module should be considered RFC 2822-conformant, especially in cases where the syntax or semantics have changed since RFC 822.