Class Charset

Lib/email/charset.py:162–398

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

class 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.
    """
    def __init__(self, input_charset=DEFAULT_CHARSET):
        # RFC 2046, $4.1.2 says charsets are not case sensitive.  We coerce to
        # unicode because its .lower() is locale insensitive.  If the argument
        # is already a unicode, we leave it at that, but ensure that the
        # charset is ASCII, as the standard (RFC XXX) requires.
        try:
            if isinstance(input_charset, str):
                input_charset.encode('ascii')
            else:
                input_charset = str(input_charset, 'ascii')
        except UnicodeError:
            raise errors.CharsetError(input_charset)
        input_charset = input_charset.lower()
        # Set the input charset after filtering through the aliases