1 :mod:`email.charset`: Representing character sets 2 ------------------------------------------------- 3 4 .. module:: email.charset 5 :synopsis: Character Sets 6 7 8 This module provides a class :class:`Charset` for representing character sets 9 and character set conversions in email messages, as well as a character set 10 registry and several convenience methods for manipulating this registry. 11 Instances of :class:`Charset` are used in several other modules within the 12 :mod:`email` package. 13 14 Import this class from the :mod:`email.charset` module. 15 16 .. versionadded:: 2.2.2 17 18 19 .. class:: Charset([input_charset]) 20 21 Map character sets to their email properties. 22 23 This class provides information about the requirements imposed on email for a 24 specific character set. It also provides convenience routines for converting 25 between character sets, given the availability of the applicable codecs. Given 26 a character set, it will do its best to provide information on how to use that 27 character set in an email message in an RFC-compliant way. 28 29 Certain character sets must be encoded with quoted-printable or base64 when used 30 in email headers or bodies. Certain character sets must be converted outright, 31 and are not allowed in email. 32 33 Optional *input_charset* is as described below; it is always coerced to lower 34 case. After being alias normalized it is also used as a lookup into the 35 registry of character sets to find out the header encoding, body encoding, and 36 output conversion codec to be used for the character set. For example, if 37 *input_charset* is ``iso-8859-1``, then headers and bodies will be encoded using 38 quoted-printable and no output conversion codec is necessary. If 39 *input_charset* is ``euc-jp``, then headers will be encoded with base64, bodies 40 will not be encoded, but output text will be converted from the ``euc-jp`` 41 character set to the ``iso-2022-jp`` character set. 42 43 :class:`Charset` instances have the following data attributes: 44 45 46 .. attribute:: input_charset 47 48 The initial character set specified. Common aliases are converted to 49 their *official* email names (e.g. ``latin_1`` is converted to 50 ``iso-8859-1``). Defaults to 7-bit ``us-ascii``. 51 52 53 .. attribute:: header_encoding 54 55 If the character set must be encoded before it can be used in an email 56 header, this attribute will be set to ``Charset.QP`` (for 57 quoted-printable), ``Charset.BASE64`` (for base64 encoding), or 58 ``Charset.SHORTEST`` for the shortest of QP or BASE64 encoding. Otherwise, 59 it will be ``None``. 60 61 62 .. attribute:: body_encoding 63 64 Same as *header_encoding*, but describes the encoding for the mail 65 message's body, which indeed may be different than the header encoding. 66 ``Charset.SHORTEST`` is not allowed for *body_encoding*. 67 68 69 .. attribute:: output_charset 70 71 Some character sets must be converted before they can be used in email headers 72 or bodies. If the *input_charset* is one of them, this attribute will 73 contain the name of the character set output will be converted to. Otherwise, it will 74 be ``None``. 75 76 77 .. attribute:: input_codec 78 79 The name of the Python codec used to convert the *input_charset* to 80 Unicode. If no conversion codec is necessary, this attribute will be 81 ``None``. 82 83 84 .. attribute:: output_codec 85 86 The name of the Python codec used to convert Unicode to the 87 *output_charset*. If no conversion codec is necessary, this attribute 88 will have the same value as the *input_codec*. 89 90 :class:`Charset` instances also have the following methods: 91 92 93 .. method:: get_body_encoding() 94 95 Return the content transfer encoding used for body encoding. 96 97 This is either the string ``quoted-printable`` or ``base64`` depending on 98 the encoding used, or it is a function, in which case you should call the 99 function with a single argument, the Message object being encoded. The 100 function should then set the :mailheader:`Content-Transfer-Encoding` 101 header itself to whatever is appropriate. 102 103 Returns the string ``quoted-printable`` if *body_encoding* is ``QP``, 104 returns the string ``base64`` if *body_encoding* is ``BASE64``, and 105 returns the string ``7bit`` otherwise. 106 107 108 .. method:: convert(s) 109 110 Convert the string *s* from the *input_codec* to the *output_codec*. 111 112 113 .. method:: to_splittable(s) 114 115 Convert a possibly multibyte string to a safely splittable format. *s* is 116 the string to split. 117 118 Uses the *input_codec* to try and convert the string to Unicode, so it can 119 be safely split on character boundaries (even for multibyte characters). 120 121 Returns the string as-is if it isn't known how to convert *s* to Unicode 122 with the *input_charset*. 123 124 Characters that could not be converted to Unicode will be replaced with 125 the Unicode replacement character ``'U+FFFD'``. 126 127 128 .. method:: from_splittable(ustr[, to_output]) 129 130 Convert a splittable string back into an encoded string. *ustr* is a 131 Unicode string to "unsplit". 132 133 This method uses the proper codec to try and convert the string from 134 Unicode back into an encoded format. Return the string as-is if it is not 135 Unicode, or if it could not be converted from Unicode. 136 137 Characters that could not be converted from Unicode will be replaced with 138 an appropriate character (usually ``'?'``). 139 140 If *to_output* is ``True`` (the default), uses *output_codec* to convert 141 to an encoded format. If *to_output* is ``False``, it uses *input_codec*. 142 143 144 .. method:: get_output_charset() 145 146 Return the output character set. 147 148 This is the *output_charset* attribute if that is not ``None``, otherwise 149 it is *input_charset*. 150 151 152 .. method:: encoded_header_len() 153 154 Return the length of the encoded header string, properly calculating for 155 quoted-printable or base64 encoding. 156 157 158 .. method:: header_encode(s[, convert]) 159 160 Header-encode the string *s*. 161 162 If *convert* is ``True``, the string will be converted from the input 163 charset to the output charset automatically. This is not useful for 164 multibyte character sets, which have line length issues (multibyte 165 characters must be split on a character, not a byte boundary); use the 166 higher-level :class:`~email.header.Header` class to deal with these issues 167 (see :mod:`email.header`). *convert* defaults to ``False``. 168 169 The type of encoding (base64 or quoted-printable) will be based on the 170 *header_encoding* attribute. 171 172 173 .. method:: body_encode(s[, convert]) 174 175 Body-encode the string *s*. 176 177 If *convert* is ``True`` (the default), the string will be converted from 178 the input charset to output charset automatically. Unlike 179 :meth:`header_encode`, there are no issues with byte boundaries and 180 multibyte charsets in email bodies, so this is usually pretty safe. 181 182 The type of encoding (base64 or quoted-printable) will be based on the 183 *body_encoding* attribute. 184 185 The :class:`Charset` class also provides a number of methods to support 186 standard operations and built-in functions. 187 188 189 .. method:: __str__() 190 191 Returns *input_charset* as a string coerced to lower 192 case. :meth:`__repr__` is an alias for :meth:`__str__`. 193 194 195 .. method:: __eq__(other) 196 197 This method allows you to compare two :class:`Charset` instances for 198 equality. 199 200 201 .. method:: __ne__(other) 202 203 This method allows you to compare two :class:`Charset` instances for 204 inequality. 205 206 The :mod:`email.charset` module also provides the following functions for adding 207 new entries to the global character set, alias, and codec registries: 208 209 210 .. function:: add_charset(charset[, header_enc[, body_enc[, output_charset]]]) 211 212 Add character properties to the global registry. 213 214 *charset* is the input character set, and must be the canonical name of a 215 character set. 216 217 Optional *header_enc* and *body_enc* is either ``Charset.QP`` for 218 quoted-printable, ``Charset.BASE64`` for base64 encoding, 219 ``Charset.SHORTEST`` for the shortest of quoted-printable or base64 encoding, 220 or ``None`` for no encoding. ``SHORTEST`` is only valid for 221 *header_enc*. The default is ``None`` for no encoding. 222 223 Optional *output_charset* is the character set that the output should be in. 224 Conversions will proceed from input charset, to Unicode, to the output charset 225 when the method :meth:`Charset.convert` is called. The default is to output in 226 the same character set as the input. 227 228 Both *input_charset* and *output_charset* must have Unicode codec entries in the 229 module's character set-to-codec mapping; use :func:`add_codec` to add codecs the 230 module does not know about. See the :mod:`codecs` module's documentation for 231 more information. 232 233 The global character set registry is kept in the module global dictionary 234 ``CHARSETS``. 235 236 237 .. function:: add_alias(alias, canonical) 238 239 Add a character set alias. *alias* is the alias name, e.g. ``latin-1``. 240 *canonical* is the character set's canonical name, e.g. ``iso-8859-1``. 241 242 The global charset alias registry is kept in the module global dictionary 243 ``ALIASES``. 244 245 246 .. function:: add_codec(charset, codecname) 247 248 Add a codec that map characters in the given character set to and from Unicode. 249 250 *charset* is the canonical name of a character set. *codecname* is the name of a 251 Python codec, as appropriate for the second argument to the :func:`unicode` 252 built-in, or to the :meth:`~unicode.encode` method of a Unicode string. 253 254
