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New in version 2.3.
This module implements RFC 3490 (Internationalized Domain Names in
Applications) and RFC 3492 (Nameprep: A Stringprep Profile for
Internationalized Domain Names (IDN)). It builds upon the
punycode encoding and stringprep.
These RFCs together define a protocol to support non-ASCII characters in domain names. A domain name containing non-ASCII characters (such as ``www.Alliancefrançaise.nu'') is converted into an ASCII-compatible encoding (ACE, such as ``www.xn-alliancefranaise-npb.nu''). The ACE form of the domain name is then used in all places where arbitrary characters are not allowed by the protocol, such as DNS queries, HTTP Host: fields, and so on. This conversion is carried out in the application; if possible invisible to the user: The application should transparently convert Unicode domain labels to IDNA on the wire, and convert back ACE labels to Unicode before presenting them to the user.
Python supports this conversion in several ways: The idna codec
allows to convert between Unicode and the ACE. Furthermore, the
socket module transparently converts Unicode host names to
ACE, so that applications need not be concerned about converting host
names themselves when they pass them to the socket module. On top of
that, modules that have host names as function parameters, such as
httplib and ftplib, accept Unicode host names
(httplib then also transparently sends an IDNA hostname in
the Host: field if it sends that field at all).
When receiving host names from the wire (such as in reverse name lookup), no automatic conversion to Unicode is performed: Applications wishing to present such host names to the user should decode them to Unicode.
The module encodings.idna also implements the nameprep procedure, which performs certain normalizations on host names, to achieve case-insensitivity of international domain names, and to unify similar characters. The nameprep functions can be used directly if desired.
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AllowUnassigned is
true.
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UseSTD3ASCIIRules is assumed to be false.
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