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| 55 | <H2><A NAME="SECTION0014250000000000000000"> |
| 56 | 12.2.5 Internationalized headers</A> |
| 57 | </H2> |
| 58 | <A NAME="module-email.Header"></A> |
| 59 | |
| 60 | <P> |
| 61 | <a class="rfc" id='rfcref-90877' xml:id='rfcref-90877' |
| 62 | href="http://www.faqs.org/rfcs/rfc2822.html">RFC 2822</a> is the base standard that describes the format of email |
| 63 | messages. It derives from the older <a class="rfc" id='rfcref-90879' xml:id='rfcref-90879' |
| 64 | href="http://www.faqs.org/rfcs/rfc822.html">RFC 822</a> standard which came |
| 65 | into widespread use at a time when most email was composed of ASCII |
| 66 | characters only. <a class="rfc" id='rfcref-90881' xml:id='rfcref-90881' |
| 67 | href="http://www.faqs.org/rfcs/rfc2822.html">RFC 2822</a> is a specification written assuming email |
| 68 | contains only 7-bit ASCII characters. |
| 69 | |
| 70 | <P> |
| 71 | Of course, as email has been deployed worldwide, it has become |
| 72 | internationalized, such that language specific character sets can now |
| 73 | be used in email messages. The base standard still requires email |
| 74 | messages to be transferred using only 7-bit ASCII characters, so a |
| 75 | slew of RFCs have been written describing how to encode email |
| 76 | containing non-ASCII characters into <a class="rfc" id='rfcref-90883' xml:id='rfcref-90883' |
| 77 | href="http://www.faqs.org/rfcs/rfc2822.html">RFC 2822</a>-compliant format. |
| 78 | These RFCs include <a class="rfc" id='rfcref-90885' xml:id='rfcref-90885' |
| 79 | href="http://www.faqs.org/rfcs/rfc2045.html">RFC 2045</a>, <a class="rfc" id='rfcref-90887' xml:id='rfcref-90887' |
| 80 | href="http://www.faqs.org/rfcs/rfc2046.html">RFC 2046</a>, <a class="rfc" id='rfcref-90889' xml:id='rfcref-90889' |
| 81 | href="http://www.faqs.org/rfcs/rfc2047.html">RFC 2047</a>, and <a class="rfc" id='rfcref-90891' xml:id='rfcref-90891' |
| 82 | href="http://www.faqs.org/rfcs/rfc2231.html">RFC 2231</a>. |
| 83 | The <tt class="module">email</tt> package supports these standards in its |
| 84 | <tt class="module">email.Header</tt> and <tt class="module">email.Charset</tt> modules. |
| 85 | |
| 86 | <P> |
| 87 | If you want to include non-ASCII characters in your email headers, |
| 88 | say in the <span class="mailheader">Subject:</span> or <span class="mailheader">To:</span> fields, you should |
| 89 | use the <tt class="class">Header</tt> class and assign the field in the |
| 90 | <tt class="class">Message</tt> object to an instance of <tt class="class">Header</tt> instead of |
| 91 | using a string for the header value. For example: |
| 92 | |
| 93 | <P> |
| 94 | <div class="verbatim"><pre> |
| 95 | >>> from email.Message import Message |
| 96 | >>> from email.Header import Header |
| 97 | >>> msg = Message() |
| 98 | >>> h = Header('p\xf6stal', 'iso-8859-1') |
| 99 | >>> msg['Subject'] = h |
| 100 | >>> print msg.as_string() |
| 101 | Subject: =?iso-8859-1?q?p=F6stal?= |
| 102 | </pre></div> |
| 103 | |
| 104 | <P> |
| 105 | Notice here how we wanted the <span class="mailheader">Subject:</span> field to contain a |
| 106 | non-ASCII character? We did this by creating a <tt class="class">Header</tt> |
| 107 | instance and passing in the character set that the byte string was |
| 108 | encoded in. When the subsequent <tt class="class">Message</tt> instance was |
| 109 | flattened, the <span class="mailheader">Subject:</span> field was properly <a class="rfc" id='rfcref-90893' xml:id='rfcref-90893' |
| 110 | href="http://www.faqs.org/rfcs/rfc2047.html">RFC 2047</a> |
| 111 | encoded. MIME-aware mail readers would show this header using the |
| 112 | embedded ISO-8859-1 character. |
| 113 | |
| 114 | <P> |
| 115 | |
| 116 | <span class="versionnote">New in version 2.2.2.</span> |
| 117 | |
| 118 | <P> |
| 119 | Here is the <tt class="class">Header</tt> class description: |
| 120 | |
| 121 | <P> |
| 122 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 123 | <td><nobr><b><span class="typelabel">class</span> <tt id='l2h-3899' xml:id='l2h-3899' class="class">Header</tt></b>(</nobr></td> |
| 124 | <td><var></var><big>[</big><var>s</var><big>[</big><var>, charset</var><big>[</big><var>, |
| 125 | maxlinelen</var><big>[</big><var>, header_name</var><big>[</big><var>, continuation_ws</var><big>[</big><var>, |
| 126 | errors</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> |
| 127 | <dd> |
| 128 | Create a MIME-compliant header that can contain strings in different |
| 129 | character sets. |
| 130 | |
| 131 | <P> |
| 132 | Optional <var>s</var> is the initial header value. If <code>None</code> (the |
| 133 | default), the initial header value is not set. You can later append |
| 134 | to the header with <tt class="method">append()</tt> method calls. <var>s</var> may be a |
| 135 | byte string or a Unicode string, but see the <tt class="method">append()</tt> |
| 136 | documentation for semantics. |
| 137 | |
| 138 | <P> |
| 139 | Optional <var>charset</var> serves two purposes: it has the same meaning as |
| 140 | the <var>charset</var> argument to the <tt class="method">append()</tt> method. It also |
| 141 | sets the default character set for all subsequent <tt class="method">append()</tt> |
| 142 | calls that omit the <var>charset</var> argument. If <var>charset</var> is not |
| 143 | provided in the constructor (the default), the <code>us-ascii</code> |
| 144 | character set is used both as <var>s</var>'s initial charset and as the |
| 145 | default for subsequent <tt class="method">append()</tt> calls. |
| 146 | |
| 147 | <P> |
| 148 | The maximum line length can be specified explicit via |
| 149 | <var>maxlinelen</var>. For splitting the first line to a shorter value (to |
| 150 | account for the field header which isn't included in <var>s</var>, |
| 151 | e.g. <span class="mailheader">Subject:</span>) pass in the name of the field in |
| 152 | <var>header_name</var>. The default <var>maxlinelen</var> is 76, and the |
| 153 | default value for <var>header_name</var> is <code>None</code>, meaning it is not |
| 154 | taken into account for the first line of a long, split header. |
| 155 | |
| 156 | <P> |
| 157 | Optional <var>continuation_ws</var> must be <a class="rfc" id='rfcref-90895' xml:id='rfcref-90895' |
| 158 | href="http://www.faqs.org/rfcs/rfc2822.html">RFC 2822</a>-compliant folding |
| 159 | whitespace, and is usually either a space or a hard tab character. |
| 160 | This character will be prepended to continuation lines. |
| 161 | </dl> |
| 162 | |
| 163 | <P> |
| 164 | Optional <var>errors</var> is passed straight through to the |
| 165 | <tt class="method">append()</tt> method. |
| 166 | |
| 167 | <P> |
| 168 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 169 | <td><nobr><b><tt id='l2h-3900' xml:id='l2h-3900' class="method">append</tt></b>(</nobr></td> |
| 170 | <td><var>s</var><big>[</big><var>, charset</var><big>[</big><var>, errors</var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> |
| 171 | <dd> |
| 172 | Append the string <var>s</var> to the MIME header. |
| 173 | |
| 174 | <P> |
| 175 | Optional <var>charset</var>, if given, should be a <tt class="class">Charset</tt> instance |
| 176 | (see <tt class="module"><a href="module-email.Charset.html">email.Charset</a></tt>) or the name of a character set, which |
| 177 | will be converted to a <tt class="class">Charset</tt> instance. A value of |
| 178 | <code>None</code> (the default) means that the <var>charset</var> given in the |
| 179 | constructor is used. |
| 180 | |
| 181 | <P> |
| 182 | <var>s</var> may be a byte string or a Unicode string. If it is a byte |
| 183 | string (i.e. <code>isinstance(s, str)</code> is true), then |
| 184 | <var>charset</var> is the encoding of that byte string, and a |
| 185 | <tt class="exception">UnicodeError</tt> will be raised if the string cannot be |
| 186 | decoded with that character set. |
| 187 | |
| 188 | <P> |
| 189 | If <var>s</var> is a Unicode string, then <var>charset</var> is a hint |
| 190 | specifying the character set of the characters in the string. In this |
| 191 | case, when producing an <a class="rfc" id='rfcref-90897' xml:id='rfcref-90897' |
| 192 | href="http://www.faqs.org/rfcs/rfc2822.html">RFC 2822</a>-compliant header using <a class="rfc" id='rfcref-90899' xml:id='rfcref-90899' |
| 193 | href="http://www.faqs.org/rfcs/rfc2047.html">RFC 2047</a> |
| 194 | rules, the Unicode string will be encoded using the following charsets |
| 195 | in order: <code>us-ascii</code>, the <var>charset</var> hint, <code>utf-8</code>. The |
| 196 | first character set to not provoke a <tt class="exception">UnicodeError</tt> is used. |
| 197 | |
| 198 | <P> |
| 199 | Optional <var>errors</var> is passed through to any <tt class="function">unicode()</tt> or |
| 200 | <tt class="function">ustr.encode()</tt> call, and defaults to ``strict''. |
| 201 | </dl> |
| 202 | |
| 203 | <P> |
| 204 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 205 | <td><nobr><b><tt id='l2h-3901' xml:id='l2h-3901' class="method">encode</tt></b>(</nobr></td> |
| 206 | <td><var></var><big>[</big><var>splitchars</var><big>]</big><var></var>)</td></tr></table></dt> |
| 207 | <dd> |
| 208 | Encode a message header into an RFC-compliant format, possibly |
| 209 | wrapping long lines and encapsulating non-ASCII parts in base64 or |
| 210 | quoted-printable encodings. Optional <var>splitchars</var> is a string |
| 211 | containing characters to split long ASCII lines on, in rough support |
| 212 | of <a class="rfc" id='rfcref-90901' xml:id='rfcref-90901' |
| 213 | href="http://www.faqs.org/rfcs/rfc2822.html">RFC 2822</a>'s <em>highest level syntactic breaks</em>. This doesn't |
| 214 | affect <a class="rfc" id='rfcref-90903' xml:id='rfcref-90903' |
| 215 | href="http://www.faqs.org/rfcs/rfc2047.html">RFC 2047</a> encoded lines. |
| 216 | </dl> |
| 217 | |
| 218 | <P> |
| 219 | The <tt class="class">Header</tt> class also provides a number of methods to support |
| 220 | standard operators and built-in functions. |
| 221 | |
| 222 | <P> |
| 223 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 224 | <td><nobr><b><tt id='l2h-3902' xml:id='l2h-3902' class="method">__str__</tt></b>(</nobr></td> |
| 225 | <td><var></var>)</td></tr></table></dt> |
| 226 | <dd> |
| 227 | A synonym for <tt class="method">Header.encode()</tt>. Useful for |
| 228 | <code>str(aHeader)</code>. |
| 229 | </dl> |
| 230 | |
| 231 | <P> |
| 232 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 233 | <td><nobr><b><tt id='l2h-3903' xml:id='l2h-3903' class="method">__unicode__</tt></b>(</nobr></td> |
| 234 | <td><var></var>)</td></tr></table></dt> |
| 235 | <dd> |
| 236 | A helper for the built-in <tt class="function">unicode()</tt> function. Returns the |
| 237 | header as a Unicode string. |
| 238 | </dl> |
| 239 | |
| 240 | <P> |
| 241 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 242 | <td><nobr><b><tt id='l2h-3904' xml:id='l2h-3904' class="method">__eq__</tt></b>(</nobr></td> |
| 243 | <td><var>other</var>)</td></tr></table></dt> |
| 244 | <dd> |
| 245 | This method allows you to compare two <tt class="class">Header</tt> instances for equality. |
| 246 | </dl> |
| 247 | |
| 248 | <P> |
| 249 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 250 | <td><nobr><b><tt id='l2h-3905' xml:id='l2h-3905' class="method">__ne__</tt></b>(</nobr></td> |
| 251 | <td><var>other</var>)</td></tr></table></dt> |
| 252 | <dd> |
| 253 | This method allows you to compare two <tt class="class">Header</tt> instances for inequality. |
| 254 | </dl> |
| 255 | |
| 256 | <P> |
| 257 | The <tt class="module">email.Header</tt> module also provides the following |
| 258 | convenient functions. |
| 259 | |
| 260 | <P> |
| 261 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 262 | <td><nobr><b><tt id='l2h-3906' xml:id='l2h-3906' class="function">decode_header</tt></b>(</nobr></td> |
| 263 | <td><var>header</var>)</td></tr></table></dt> |
| 264 | <dd> |
| 265 | Decode a message header value without converting the character set. |
| 266 | The header value is in <var>header</var>. |
| 267 | |
| 268 | <P> |
| 269 | This function returns a list of <code>(decoded_string, charset)</code> pairs |
| 270 | containing each of the decoded parts of the header. <var>charset</var> is |
| 271 | <code>None</code> for non-encoded parts of the header, otherwise a lower |
| 272 | case string containing the name of the character set specified in the |
| 273 | encoded string. |
| 274 | |
| 275 | <P> |
| 276 | Here's an example: |
| 277 | |
| 278 | <P> |
| 279 | <div class="verbatim"><pre> |
| 280 | >>> from email.Header import decode_header |
| 281 | >>> decode_header('=?iso-8859-1?q?p=F6stal?=') |
| 282 | [('p\xf6stal', 'iso-8859-1')] |
| 283 | </pre></div> |
| 284 | </dl> |
| 285 | |
| 286 | <P> |
| 287 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 288 | <td><nobr><b><tt id='l2h-3907' xml:id='l2h-3907' class="function">make_header</tt></b>(</nobr></td> |
| 289 | <td><var>decoded_seq</var><big>[</big><var>, maxlinelen</var><big>[</big><var>, |
| 290 | header_name</var><big>[</big><var>, continuation_ws</var><big>]</big><var></var><big>]</big><var></var><big>]</big><var></var>)</td></tr></table></dt> |
| 291 | <dd> |
| 292 | Create a <tt class="class">Header</tt> instance from a sequence of pairs as returned |
| 293 | by <tt class="function">decode_header()</tt>. |
| 294 | |
| 295 | <P> |
| 296 | <tt class="function">decode_header()</tt> takes a header value string and returns a |
| 297 | sequence of pairs of the format <code>(decoded_string, charset)</code> where |
| 298 | <var>charset</var> is the name of the character set. |
| 299 | |
| 300 | <P> |
| 301 | This function takes one of those sequence of pairs and returns a |
| 302 | <tt class="class">Header</tt> instance. Optional <var>maxlinelen</var>, |
| 303 | <var>header_name</var>, and <var>continuation_ws</var> are as in the |
| 304 | <tt class="class">Header</tt> constructor. |
| 305 | </dl> |
| 306 | |
| 307 | <P> |
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| 343 | <span class="release-info">Release 2.4.2, documentation updated on 28 September 2005.</span> |
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