1:mod:`email.charset`: Representing character sets 2------------------------------------------------- 3 4.. module:: email.charset 5 :synopsis: Character Sets 6 7**Source code:** :source:`Lib/email/charset.py` 8 9-------------- 10 11This module is part of the legacy (``Compat32``) email API. In the new 12API only the aliases table is used. 13 14The remaining text in this section is the original documentation of the module. 15 16This module provides a class :class:`Charset` for representing character sets 17and character set conversions in email messages, as well as a character set 18registry and several convenience methods for manipulating this registry. 19Instances of :class:`Charset` are used in several other modules within the 20:mod:`email` package. 21 22Import this class from the :mod:`email.charset` module. 23 24 25.. class:: Charset(input_charset=DEFAULT_CHARSET) 26 27 Map character sets to their email properties. 28 29 This class provides information about the requirements imposed on email for a 30 specific character set. It also provides convenience routines for converting 31 between character sets, given the availability of the applicable codecs. Given 32 a character set, it will do its best to provide information on how to use that 33 character set in an email message in an RFC-compliant way. 34 35 Certain character sets must be encoded with quoted-printable or base64 when used 36 in email headers or bodies. Certain character sets must be converted outright, 37 and are not allowed in email. 38 39 Optional *input_charset* is as described below; it is always coerced to lower 40 case. After being alias normalized it is also used as a lookup into the 41 registry of character sets to find out the header encoding, body encoding, and 42 output conversion codec to be used for the character set. For example, if 43 *input_charset* is ``iso-8859-1``, then headers and bodies will be encoded using 44 quoted-printable and no output conversion codec is necessary. If 45 *input_charset* is ``euc-jp``, then headers will be encoded with base64, bodies 46 will not be encoded, but output text will be converted from the ``euc-jp`` 47 character set to the ``iso-2022-jp`` character set. 48 49 :class:`Charset` instances have the following data attributes: 50 51 .. attribute:: input_charset 52 53 The initial character set specified. Common aliases are converted to 54 their *official* email names (e.g. ``latin_1`` is converted to 55 ``iso-8859-1``). Defaults to 7-bit ``us-ascii``. 56 57 58 .. attribute:: header_encoding 59 60 If the character set must be encoded before it can be used in an email 61 header, this attribute will be set to ``Charset.QP`` (for 62 quoted-printable), ``Charset.BASE64`` (for base64 encoding), or 63 ``Charset.SHORTEST`` for the shortest of QP or BASE64 encoding. Otherwise, 64 it will be ``None``. 65 66 67 .. attribute:: body_encoding 68 69 Same as *header_encoding*, but describes the encoding for the mail 70 message's body, which indeed may be different than the header encoding. 71 ``Charset.SHORTEST`` is not allowed for *body_encoding*. 72 73 74 .. attribute:: output_charset 75 76 Some character sets must be converted before they can be used in email 77 headers or bodies. If the *input_charset* is one of them, this attribute 78 will contain the name of the character set output will be converted to. 79 Otherwise, it will be ``None``. 80 81 82 .. attribute:: input_codec 83 84 The name of the Python codec used to convert the *input_charset* to 85 Unicode. If no conversion codec is necessary, this attribute will be 86 ``None``. 87 88 89 .. attribute:: output_codec 90 91 The name of the Python codec used to convert Unicode to the 92 *output_charset*. If no conversion codec is necessary, this attribute 93 will have the same value as the *input_codec*. 94 95 96 :class:`Charset` instances also have the following methods: 97 98 .. method:: get_body_encoding() 99 100 Return the content transfer encoding used for body encoding. 101 102 This is either the string ``quoted-printable`` or ``base64`` depending on 103 the encoding used, or it is a function, in which case you should call the 104 function with a single argument, the Message object being encoded. The 105 function should then set the :mailheader:`Content-Transfer-Encoding` 106 header itself to whatever is appropriate. 107 108 Returns the string ``quoted-printable`` if *body_encoding* is ``QP``, 109 returns the string ``base64`` if *body_encoding* is ``BASE64``, and 110 returns the string ``7bit`` otherwise. 111 112 113 .. method:: get_output_charset() 114 115 Return the output character set. 116 117 This is the *output_charset* attribute if that is not ``None``, otherwise 118 it is *input_charset*. 119 120 121 .. method:: header_encode(string) 122 123 Header-encode the string *string*. 124 125 The type of encoding (base64 or quoted-printable) will be based on the 126 *header_encoding* attribute. 127 128 129 .. method:: header_encode_lines(string, maxlengths) 130 131 Header-encode a *string* by converting it first to bytes. 132 133 This is similar to :meth:`header_encode` except that the string is fit 134 into maximum line lengths as given by the argument *maxlengths*, which 135 must be an iterator: each element returned from this iterator will provide 136 the next maximum line length. 137 138 139 .. method:: body_encode(string) 140 141 Body-encode the string *string*. 142 143 The type of encoding (base64 or quoted-printable) will be based on the 144 *body_encoding* attribute. 145 146 The :class:`Charset` class also provides a number of methods to support 147 standard operations and built-in functions. 148 149 150 .. method:: __str__() 151 152 Returns *input_charset* as a string coerced to lower 153 case. :meth:`__repr__` is an alias for :meth:`__str__`. 154 155 156 .. method:: __eq__(other) 157 158 This method allows you to compare two :class:`Charset` instances for 159 equality. 160 161 162 .. method:: __ne__(other) 163 164 This method allows you to compare two :class:`Charset` instances for 165 inequality. 166 167The :mod:`email.charset` module also provides the following functions for adding 168new entries to the global character set, alias, and codec registries: 169 170 171.. function:: add_charset(charset, header_enc=None, body_enc=None, output_charset=None) 172 173 Add character properties to the global registry. 174 175 *charset* is the input character set, and must be the canonical name of a 176 character set. 177 178 Optional *header_enc* and *body_enc* is either ``Charset.QP`` for 179 quoted-printable, ``Charset.BASE64`` for base64 encoding, 180 ``Charset.SHORTEST`` for the shortest of quoted-printable or base64 encoding, 181 or ``None`` for no encoding. ``SHORTEST`` is only valid for 182 *header_enc*. The default is ``None`` for no encoding. 183 184 Optional *output_charset* is the character set that the output should be in. 185 Conversions will proceed from input charset, to Unicode, to the output charset 186 when the method :meth:`Charset.convert` is called. The default is to output in 187 the same character set as the input. 188 189 Both *input_charset* and *output_charset* must have Unicode codec entries in the 190 module's character set-to-codec mapping; use :func:`add_codec` to add codecs the 191 module does not know about. See the :mod:`codecs` module's documentation for 192 more information. 193 194 The global character set registry is kept in the module global dictionary 195 ``CHARSETS``. 196 197 198.. function:: add_alias(alias, canonical) 199 200 Add a character set alias. *alias* is the alias name, e.g. ``latin-1``. 201 *canonical* is the character set's canonical name, e.g. ``iso-8859-1``. 202 203 The global charset alias registry is kept in the module global dictionary 204 ``ALIASES``. 205 206 207.. function:: add_codec(charset, codecname) 208 209 Add a codec that map characters in the given character set to and from Unicode. 210 211 *charset* is the canonical name of a character set. *codecname* is the name of a 212 Python codec, as appropriate for the second argument to the :class:`str`'s 213 :meth:`~str.encode` method. 214 215