mirror of
https://github.com/python/cpython.git
synced 2024-11-30 05:15:14 +08:00
235 lines
8.6 KiB
ReStructuredText
235 lines
8.6 KiB
ReStructuredText
:mod:`email`: Representing character sets
|
|
-----------------------------------------
|
|
|
|
.. module:: email.charset
|
|
:synopsis: Character Sets
|
|
|
|
|
|
This module provides a class :class:`Charset` for representing character sets
|
|
and character set conversions in email messages, as well as a character set
|
|
registry and several convenience methods for manipulating this registry.
|
|
Instances of :class:`Charset` are used in several other modules within the
|
|
:mod:`email` package.
|
|
|
|
Import this class from the :mod:`email.charset` module.
|
|
|
|
|
|
.. class:: Charset(input_charset=DEFAULT_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 message 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.
|
|
|
|
Optional *input_charset* is as described below; it is always coerced to lower
|
|
case. After being alias normalized it is also used as a lookup into the
|
|
registry of character sets to find out the header encoding, body encoding, and
|
|
output conversion codec to be used for the character set. For example, if
|
|
*input_charset* is ``iso-8859-1``, then headers and bodies will be encoded using
|
|
quoted-printable and no output conversion codec is necessary. If
|
|
*input_charset* is ``euc-jp``, then headers will be encoded with base64, bodies
|
|
will not be encoded, but output text will be converted from the ``euc-jp``
|
|
character set to the ``iso-2022-jp`` character set.
|
|
|
|
:class:`Charset` instances have the following data attributes:
|
|
|
|
.. attribute:: 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``.
|
|
|
|
|
|
.. attribute:: 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``.
|
|
|
|
|
|
.. attribute:: 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*.
|
|
|
|
|
|
.. attribute:: 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 character set output will be converted to.
|
|
Otherwise, it will be ``None``.
|
|
|
|
|
|
.. attribute:: 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``.
|
|
|
|
|
|
.. attribute:: 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*.
|
|
|
|
|
|
:class:`Charset` instances also have the following methods:
|
|
|
|
.. method:: get_body_encoding()
|
|
|
|
Return the content transfer encoding used for body encoding.
|
|
|
|
This is either the string ``quoted-printable`` or ``base64`` depending on
|
|
the encoding used, or it is a function, in which case you should call the
|
|
function with a single argument, the Message object being encoded. The
|
|
function should then set the :mailheader:`Content-Transfer-Encoding`
|
|
header itself to whatever is appropriate.
|
|
|
|
Returns the string ``quoted-printable`` if *body_encoding* is ``QP``,
|
|
returns the string ``base64`` if *body_encoding* is ``BASE64``, and
|
|
returns the string ``7bit`` otherwise.
|
|
|
|
.. XXX to_splittable and from_splittable are not there anymore!
|
|
|
|
.. method to_splittable(s)
|
|
|
|
Convert a possibly multibyte string to a safely splittable format. *s* is
|
|
the string to split.
|
|
|
|
Uses the *input_codec* to try and convert the string to Unicode, so it can
|
|
be safely split on character boundaries (even for multibyte characters).
|
|
|
|
Returns the string as-is if it isn't known how to convert *s* to Unicode
|
|
with the *input_charset*.
|
|
|
|
Characters that could not be converted to Unicode will be replaced with
|
|
the Unicode replacement character ``'U+FFFD'``.
|
|
|
|
|
|
.. method from_splittable(ustr[, to_output])
|
|
|
|
Convert a splittable string back into an encoded string. *ustr* is a
|
|
Unicode string to "unsplit".
|
|
|
|
This method uses the proper codec to try and convert the string from
|
|
Unicode back into an encoded format. Return the string as-is if it is not
|
|
Unicode, or if it could not be converted from Unicode.
|
|
|
|
Characters that could not be converted from Unicode will be replaced with
|
|
an appropriate character (usually ``'?'``).
|
|
|
|
If *to_output* is ``True`` (the default), uses *output_codec* to convert
|
|
to an encoded format. If *to_output* is ``False``, it uses *input_codec*.
|
|
|
|
|
|
.. method:: get_output_charset()
|
|
|
|
Return the output character set.
|
|
|
|
This is the *output_charset* attribute if that is not ``None``, otherwise
|
|
it is *input_charset*.
|
|
|
|
|
|
.. method:: encoded_header_len()
|
|
|
|
Return the length of the encoded header string, properly calculating for
|
|
quoted-printable or base64 encoding.
|
|
|
|
|
|
.. method:: header_encode(string)
|
|
|
|
Header-encode the string *string*.
|
|
|
|
The type of encoding (base64 or quoted-printable) will be based on the
|
|
*header_encoding* attribute.
|
|
|
|
|
|
.. method:: body_encode(string)
|
|
|
|
Body-encode the string *string*.
|
|
|
|
The type of encoding (base64 or quoted-printable) will be based on the
|
|
*body_encoding* attribute.
|
|
|
|
The :class:`Charset` class also provides a number of methods to support
|
|
standard operations and built-in functions.
|
|
|
|
|
|
.. method:: __str__()
|
|
|
|
Returns *input_charset* as a string coerced to lower
|
|
case. :meth:`__repr__` is an alias for :meth:`__str__`.
|
|
|
|
|
|
.. method:: __eq__(other)
|
|
|
|
This method allows you to compare two :class:`Charset` instances for
|
|
equality.
|
|
|
|
|
|
.. method:: __ne__(other)
|
|
|
|
This method allows you to compare two :class:`Charset` instances for
|
|
inequality.
|
|
|
|
The :mod:`email.charset` module also provides the following functions for adding
|
|
new entries to the global character set, alias, and codec registries:
|
|
|
|
|
|
.. function:: add_charset(charset, header_enc=None, body_enc=None, output_charset=None)
|
|
|
|
Add character properties to the global registry.
|
|
|
|
*charset* is the input character set, and must be the canonical name of a
|
|
character set.
|
|
|
|
Optional *header_enc* and *body_enc* is either ``Charset.QP`` for
|
|
quoted-printable, ``Charset.BASE64`` for base64 encoding,
|
|
``Charset.SHORTEST`` for the shortest of quoted-printable or base64 encoding,
|
|
or ``None`` for no encoding. ``SHORTEST`` is only valid for
|
|
*header_enc*. The default is ``None`` for no encoding.
|
|
|
|
Optional *output_charset* is the character set that the output should be in.
|
|
Conversions will proceed from input charset, to Unicode, to the output charset
|
|
when the method :meth:`Charset.convert` is called. The default is to output in
|
|
the same character set as the input.
|
|
|
|
Both *input_charset* and *output_charset* must have Unicode codec entries in the
|
|
module's character set-to-codec mapping; use :func:`add_codec` to add codecs the
|
|
module does not know about. See the :mod:`codecs` module's documentation for
|
|
more information.
|
|
|
|
The global character set registry is kept in the module global dictionary
|
|
``CHARSETS``.
|
|
|
|
|
|
.. function:: add_alias(alias, canonical)
|
|
|
|
Add a character set alias. *alias* is the alias name, e.g. ``latin-1``.
|
|
*canonical* is the character set's canonical name, e.g. ``iso-8859-1``.
|
|
|
|
The global charset alias registry is kept in the module global dictionary
|
|
``ALIASES``.
|
|
|
|
|
|
.. function:: add_codec(charset, codecname)
|
|
|
|
Add a codec that map characters in the given character set to and from Unicode.
|
|
|
|
*charset* is the canonical name of a character set. *codecname* is the name of a
|
|
Python codec, as appropriate for the second argument to the :class:`str`'s
|
|
:func:`decode` method
|
|
|