Charset

Map character sets to their email properties.

This class provides information about the requirements imposed on email
for a specific character set.  It also provides convenience routines for
converting between character sets, given the availability of the
applicable codecs.  Given a character set, it will do its best to provide
information on how to use that character set in an email in an
RFC-compliant way.

Certain character sets must be encoded with quoted-printable or base64
when used in email headers or bodies.  Certain character sets must be
converted outright, and are not allowed in email.  Instances of this
module expose the following information about a character set:

input_charset: The initial character set specified.  Common aliases
               are converted to their 'official' email names (e.g. latin_1
               is converted to iso-8859-1).  Defaults to 7-bit us-ascii.

header_encoding: If the character set must be encoded before it can be
                 used in an email header, this attribute will be set to
                 charset.QP (for quoted-printable), charset.BASE64 (for
                 base64 encoding), or charset.SHORTEST for the shortest of
                 QP or BASE64 encoding.  Otherwise, it will be None.

body_encoding: Same as header_encoding, but describes the encoding for the
               mail message's body, which indeed may be different than the
               header encoding.  charset.SHORTEST is not allowed for
               body_encoding.

output_charset: Some character sets must be converted before they can be
                used in email headers or bodies.  If the input_charset is
                one of them, this attribute will contain the name of the
                charset output will be converted to.  Otherwise, it will
                be None.

input_codec: The name of the Python codec used to convert the
             input_charset to Unicode.  If no conversion codec is
             necessary, this attribute will be None.

output_codec: The name of the Python codec used to convert Unicode
              to the output_charset.  If no conversion codec is necessary,
              this attribute will have the same value as the input_codec.