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| 16 | <title>4.9.3 encodings.idna -- Internationalized Domain Names in Applications</title> |
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| 53 | |
| 54 | <H2><A NAME="SECTION006930000000000000000"> |
| 55 | 4.9.3 <tt class="module">encodings.idna</tt> -- |
| 56 | Internationalized Domain Names in Applications</A> |
| 57 | </H2> |
| 58 | |
| 59 | <P> |
| 60 | <A NAME="module-encodings.idna"></A> |
| 61 | |
| 62 | <P> |
| 63 | |
| 64 | <span class="versionnote">New in version 2.3.</span> |
| 65 | |
| 66 | <P> |
| 67 | This module implements <a class="rfc" id='rfcref-87091' xml:id='rfcref-87091' |
| 68 | href="http://www.faqs.org/rfcs/rfc3490.html">RFC 3490</a> (Internationalized Domain Names in |
| 69 | Applications) and <a class="rfc" id='rfcref-87093' xml:id='rfcref-87093' |
| 70 | href="http://www.faqs.org/rfcs/rfc3492.html">RFC 3492</a> (Nameprep: A Stringprep Profile for |
| 71 | Internationalized Domain Names (IDN)). It builds upon the |
| 72 | <code>punycode</code> encoding and <tt class="module"><a href="module-stringprep.html">stringprep</a></tt>. |
| 73 | |
| 74 | <P> |
| 75 | These RFCs together define a protocol to support non-ASCII characters |
| 76 | in domain names. A domain name containing non-ASCII characters (such |
| 77 | as ``www.Alliancefrançaise.nu'') is converted into an |
| 78 | ASCII-compatible encoding (ACE, such as |
| 79 | ``www.xn-alliancefranaise-npb.nu''). The ACE form of the domain name |
| 80 | is then used in all places where arbitrary characters are not allowed |
| 81 | by the protocol, such as DNS queries, HTTP <span class="mailheader">Host:</span> fields, and so |
| 82 | on. This conversion is carried out in the application; if possible |
| 83 | invisible to the user: The application should transparently convert |
| 84 | Unicode domain labels to IDNA on the wire, and convert back ACE labels |
| 85 | to Unicode before presenting them to the user. |
| 86 | |
| 87 | <P> |
| 88 | Python supports this conversion in several ways: The <code>idna</code> codec |
| 89 | allows to convert between Unicode and the ACE. Furthermore, the |
| 90 | <tt class="module"><a href="module-socket.html">socket</a></tt> module transparently converts Unicode host names to |
| 91 | ACE, so that applications need not be concerned about converting host |
| 92 | names themselves when they pass them to the socket module. On top of |
| 93 | that, modules that have host names as function parameters, such as |
| 94 | <tt class="module"><a href="module-httplib.html">httplib</a></tt> and <tt class="module"><a href="module-ftplib.html">ftplib</a></tt>, accept Unicode host names |
| 95 | (<tt class="module"><a href="module-httplib.html">httplib</a></tt> then also transparently sends an IDNA hostname in |
| 96 | the <span class="mailheader">Host:</span> field if it sends that field at all). |
| 97 | |
| 98 | <P> |
| 99 | When receiving host names from the wire (such as in reverse name |
| 100 | lookup), no automatic conversion to Unicode is performed: Applications |
| 101 | wishing to present such host names to the user should decode them to |
| 102 | Unicode. |
| 103 | |
| 104 | <P> |
| 105 | The module <tt class="module">encodings.idna</tt> also implements the nameprep |
| 106 | procedure, which performs certain normalizations on host names, to |
| 107 | achieve case-insensitivity of international domain names, and to unify |
| 108 | similar characters. The nameprep functions can be used directly if |
| 109 | desired. |
| 110 | |
| 111 | <P> |
| 112 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 113 | <td><nobr><b><tt id='l2h-1019' xml:id='l2h-1019' class="function">nameprep</tt></b>(</nobr></td> |
| 114 | <td><var>label</var>)</td></tr></table></dt> |
| 115 | <dd> |
| 116 | Return the nameprepped version of <var>label</var>. The implementation |
| 117 | currently assumes query strings, so <code>AllowUnassigned</code> is |
| 118 | true. |
| 119 | </dl> |
| 120 | |
| 121 | <P> |
| 122 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 123 | <td><nobr><b><tt id='l2h-1020' xml:id='l2h-1020' class="function">ToASCII</tt></b>(</nobr></td> |
| 124 | <td><var>label</var>)</td></tr></table></dt> |
| 125 | <dd> |
| 126 | Convert a label to ASCII, as specified in <a class="rfc" id='rfcref-87095' xml:id='rfcref-87095' |
| 127 | href="http://www.faqs.org/rfcs/rfc3490.html">RFC 3490</a>. |
| 128 | <code>UseSTD3ASCIIRules</code> is assumed to be false. |
| 129 | </dl> |
| 130 | |
| 131 | <P> |
| 132 | <dl><dt><table cellpadding="0" cellspacing="0"><tr valign="baseline"> |
| 133 | <td><nobr><b><tt id='l2h-1021' xml:id='l2h-1021' class="function">ToUnicode</tt></b>(</nobr></td> |
| 134 | <td><var>label</var>)</td></tr></table></dt> |
| 135 | <dd> |
| 136 | Convert a label to Unicode, as specified in <a class="rfc" id='rfcref-87097' xml:id='rfcref-87097' |
| 137 | href="http://www.faqs.org/rfcs/rfc3490.html">RFC 3490</a>. |
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