This module defines base classes for standard Python codecs (encoders and decoders) and provides access to the internal Python codec registry which manages the codec and error handling lookup process.
It defines the following functions:
Register a codec search function. Search functions are expected to take one argument, the encoding name in all lower case letters, and return a CodecInfo object having the following attributes:
The various functions or classes take the following arguments:
encode and decode: These must be functions or methods which have the same interface as the encode()/decode() methods of Codec instances (see Codec Interface). The functions/methods are expected to work in a stateless mode.
incrementalencoder and incrementaldecoder: These have to be factory functions providing the following interface:
factory(errors='strict')
The factory functions must return objects providing the interfaces defined by the base classes IncrementalEncoder and IncrementalDecoder, respectively. Incremental codecs can maintain state.
streamreader and streamwriter: These have to be factory functions providing the following interface:
factory(stream, errors='strict')
The factory functions must return objects providing the interfaces defined by the base classes StreamWriter and StreamReader, respectively. Stream codecs can maintain state.
Possible values for errors are 'strict' (raise an exception in case of an encoding error), 'replace' (replace malformed data with a suitable replacement marker, such as '?'), 'ignore' (ignore malformed data and continue without further notice), 'xmlcharrefreplace' (replace with the appropriate XML character reference (for encoding only)) and 'backslashreplace' (replace with backslashed escape sequences (for encoding only)) as well as any other error handling name defined via register_error().
In case a search function cannot find a given encoding, it should return None.
Looks up the codec info in the Python codec registry and returns a CodecInfo object as defined above.
Encodings are first looked up in the registry’s cache. If not found, the list of registered search functions is scanned. If no CodecInfo object is found, a LookupError is raised. Otherwise, the CodecInfo object is stored in the cache and returned to the caller.
To simplify access to the various codecs, the module provides these additional functions which use lookup() for the codec lookup:
Look up the codec for the given encoding and return its encoder function.
Raises a LookupError in case the encoding cannot be found.
Look up the codec for the given encoding and return its decoder function.
Raises a LookupError in case the encoding cannot be found.
Look up the codec for the given encoding and return its incremental encoder class or factory function.
Raises a LookupError in case the encoding cannot be found or the codec doesn’t support an incremental encoder.
Look up the codec for the given encoding and return its incremental decoder class or factory function.
Raises a LookupError in case the encoding cannot be found or the codec doesn’t support an incremental decoder.
Look up the codec for the given encoding and return its StreamReader class or factory function.
Raises a LookupError in case the encoding cannot be found.
Look up the codec for the given encoding and return its StreamWriter class or factory function.
Raises a LookupError in case the encoding cannot be found.
Register the error handling function error_handler under the name name. error_handler will be called during encoding and decoding in case of an error, when name is specified as the errors parameter.
For encoding error_handler will be called with a UnicodeEncodeError instance, which contains information about the location of the error. The error handler must either raise this or a different exception or return a tuple with a replacement for the unencodable part of the input and a position where encoding should continue. The encoder will encode the replacement and continue encoding the original input at the specified position. Negative position values will be treated as being relative to the end of the input string. If the resulting position is out of bound an IndexError will be raised.
Decoding and translating works similar, except UnicodeDecodeError or UnicodeTranslateError will be passed to the handler and that the replacement from the error handler will be put into the output directly.
Return the error handler previously registered under the name name.
Raises a LookupError in case the handler cannot be found.
To simplify working with encoded files or stream, the module also defines these utility functions:
Open an encoded file using the given mode and return a wrapped version providing transparent encoding/decoding. The default file mode is 'r' meaning to open the file in read mode.
Note
The wrapped version’s methods will accept and return strings only. Bytes arguments will be rejected.
Note
Files are always opened in binary mode, even if no binary mode was specified. This is done to avoid data loss due to encodings using 8-bit values. This means that no automatic conversion of b'\n' is done on reading and writing.
encoding specifies the encoding which is to be used for the file.
errors may be given to define the error handling. It defaults to 'strict' which causes a ValueError to be raised in case an encoding error occurs.
buffering has the same meaning as for the built-in open() function. It defaults to line buffered.
Return a wrapped version of file which provides transparent encoding translation.
Bytes written to the wrapped file are interpreted according to the given input encoding and then written to the original file as bytes using the output encoding.
If output is not given, it defaults to input.
errors may be given to define the error handling. It defaults to 'strict', which causes ValueError to be raised in case an encoding error occurs.
The module also provides the following constants which are useful for reading and writing to platform dependent files:
The codecs module defines a set of base classes which define the interface and can also be used to easily write your own codecs for use in Python.
Each codec has to define four interfaces to make it usable as codec in Python: stateless encoder, stateless decoder, stream reader and stream writer. The stream reader and writers typically reuse the stateless encoder/decoder to implement the file protocols.
The Codec class defines the interface for stateless encoders/decoders.
To simplify and standardize error handling, the encode() and decode() methods may implement different error handling schemes by providing the errors string argument. The following string values are defined and implemented by all standard Python codecs:
| Value | Meaning |
|---|---|
| 'strict' | Raise UnicodeError (or a subclass); this is the default. |
| 'ignore' | Ignore the character and continue with the next. |
| 'replace' | Replace with a suitable replacement character; Python will use the official U+FFFD REPLACEMENT CHARACTER for the built-in Unicode codecs on decoding and ‘?’ on encoding. |
| 'xmlcharrefreplace' | Replace with the appropriate XML character reference (only for encoding). |
| 'backslashreplace' | Replace with backslashed escape sequences (only for encoding). |
The set of allowed values can be extended via register_error().
The Codec class defines these methods which also define the function interfaces of the stateless encoder and decoder:
Encodes the object input and returns a tuple (output object, length consumed). Encoding converts a string object to a bytes object using a particular character set encoding (e.g., cp1252 or iso-8859-1).
errors defines the error handling to apply. It defaults to 'strict' handling.
The method may not store state in the Codec instance. Use StreamCodec for codecs which have to keep state in order to make encoding/decoding efficient.
The encoder must be able to handle zero length input and return an empty object of the output object type in this situation.
Decodes the object input and returns a tuple (output object, length consumed). Decoding converts a bytes object encoded using a particular character set encoding to a string object.
input must be a bytes object or one which provides the read-only character buffer interface – for example, buffer objects and memory mapped files.
errors defines the error handling to apply. It defaults to 'strict' handling.
The method may not store state in the Codec instance. Use StreamCodec for codecs which have to keep state in order to make encoding/decoding efficient.
The decoder must be able to handle zero length input and return an empty object of the output object type in this situation.
The IncrementalEncoder and IncrementalDecoder classes provide the basic interface for incremental encoding and decoding. Encoding/decoding the input isn’t done with one call to the stateless encoder/decoder function, but with multiple calls to the encode()/decode() method of the incremental encoder/decoder. The incremental encoder/decoder keeps track of the encoding/decoding process during method calls.
The joined output of calls to the encode()/decode() method is the same as if all the single inputs were joined into one, and this input was encoded/decoded with the stateless encoder/decoder.
The IncrementalEncoder class is used for encoding an input in multiple steps. It defines the following methods which every incremental encoder must define in order to be compatible with the Python codec registry.
Constructor for an IncrementalEncoder instance.
All incremental encoders must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.
The IncrementalEncoder may implement different error handling schemes by providing the errors keyword argument. These parameters are predefined:
The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the IncrementalEncoder object.
The set of allowed values for the errors argument can be extended with register_error().
The IncrementalDecoder class is used for decoding an input in multiple steps. It defines the following methods which every incremental decoder must define in order to be compatible with the Python codec registry.
Constructor for an IncrementalDecoder instance.
All incremental decoders must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.
The IncrementalDecoder may implement different error handling schemes by providing the errors keyword argument. These parameters are predefined:
The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the IncrementalDecoder object.
The set of allowed values for the errors argument can be extended with register_error().
The StreamWriter and StreamReader classes provide generic working interfaces which can be used to implement new encoding submodules very easily. See encodings.utf_8 for an example of how this is done.
The StreamWriter class is a subclass of Codec and defines the following methods which every stream writer must define in order to be compatible with the Python codec registry.
Constructor for a StreamWriter instance.
All stream writers must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.
stream must be a file-like object open for writing binary data.
The StreamWriter may implement different error handling schemes by providing the errors keyword argument. These parameters are predefined:
The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the StreamWriter object.
The set of allowed values for the errors argument can be extended with register_error().
Flushes and resets the codec buffers used for keeping state.
Calling this method should ensure that the data on the output is put into a clean state that allows appending of new fresh data without having to rescan the whole stream to recover state.
In addition to the above methods, the StreamWriter must also inherit all other methods and attributes from the underlying stream.
The StreamReader class is a subclass of Codec and defines the following methods which every stream reader must define in order to be compatible with the Python codec registry.
Constructor for a StreamReader instance.
All stream readers must provide this constructor interface. They are free to add additional keyword arguments, but only the ones defined here are used by the Python codec registry.
stream must be a file-like object open for reading (binary) data.
The StreamReader may implement different error handling schemes by providing the errors keyword argument. These parameters are defined:
The errors argument will be assigned to an attribute of the same name. Assigning to this attribute makes it possible to switch between different error handling strategies during the lifetime of the StreamReader object.
The set of allowed values for the errors argument can be extended with register_error().
Decodes data from the stream and returns the resulting object.
chars indicates the number of characters to read from the stream. read() will never return more than chars characters, but it might return less, if there are not enough characters available.
size indicates the approximate maximum number of bytes to read from the stream for decoding purposes. The decoder can modify this setting as appropriate. The default value -1 indicates to read and decode as much as possible. size is intended to prevent having to decode huge files in one step.
firstline indicates that it would be sufficient to only return the first line, if there are decoding errors on later lines.
The method should use a greedy read strategy meaning that it should read as much data as is allowed within the definition of the encoding and the given size, e.g. if optional encoding endings or state markers are available on the stream, these should be read too.
Read one line from the input stream and return the decoded data.
size, if given, is passed as size argument to the stream’s readline() method.
If keepends is false line-endings will be stripped from the lines returned.
Read all lines available on the input stream and return them as a list of lines.
Line-endings are implemented using the codec’s decoder method and are included in the list entries if keepends is true.
sizehint, if given, is passed as the size argument to the stream’s read() method.
Resets the codec buffers used for keeping state.
Note that no stream repositioning should take place. This method is primarily intended to be able to recover from decoding errors.
In addition to the above methods, the StreamReader must also inherit all other methods and attributes from the underlying stream.
The next two base classes are included for convenience. They are not needed by the codec registry, but may provide useful in practice.
The StreamReaderWriter allows wrapping streams which work in both read and write modes.
The design is such that one can use the factory functions returned by the lookup() function to construct the instance.
StreamReaderWriter instances define the combined interfaces of StreamReader and StreamWriter classes. They inherit all other methods and attributes from the underlying stream.
The StreamRecoder provide a frontend - backend view of encoding data which is sometimes useful when dealing with different encoding environments.
The design is such that one can use the factory functions returned by the lookup() function to construct the instance.
Creates a StreamRecoder instance which implements a two-way conversion: encode and decode work on the frontend (the input to read() and output of write()) while Reader and Writer work on the backend (reading and writing to the stream).
You can use these objects to do transparent direct recodings from e.g. Latin-1 to UTF-8 and back.
stream must be a file-like object.
encode, decode must adhere to the Codec interface. Reader, Writer must be factory functions or classes providing objects of the StreamReader and StreamWriter interface respectively.
encode and decode are needed for the frontend translation, Reader and Writer for the backend translation.
Error handling is done in the same way as defined for the stream readers and writers.
StreamRecoder instances define the combined interfaces of StreamReader and StreamWriter classes. They inherit all other methods and attributes from the underlying stream.
Strings are stored internally as sequences of codepoints (to be precise as Py_UNICODE arrays). Depending on the way Python is compiled (either via --without-wide-unicode or --with-wide-unicode, with the former being the default) Py_UNICODE is either a 16-bit or 32-bit data type. Once a string object is used outside of CPU and memory, CPU endianness and how these arrays are stored as bytes become an issue. Transforming a string object into a sequence of bytes is called encoding and recreating the string object from the sequence of bytes is known as decoding. There are many different methods for how this transformation can be done (these methods are also called encodings). The simplest method is to map the codepoints 0-255 to the bytes 0x0-0xff. This means that a string object that contains codepoints above U+00FF can’t be encoded with this method (which is called 'latin-1' or 'iso-8859-1'). str.encode() will raise a UnicodeEncodeError that looks like this: UnicodeEncodeError: 'latin-1' codec can't encode character '\u1234' in position 3: ordinal not in range(256).
There’s another group of encodings (the so called charmap encodings) that choose a different subset of all Unicode code points and how these codepoints are mapped to the bytes 0x0-0xff. To see how this is done simply open e.g. encodings/cp1252.py (which is an encoding that is used primarily on Windows). There’s a string constant with 256 characters that shows you which character is mapped to which byte value.
All of these encodings can only encode 256 of the 65536 (or 1114111) codepoints defined in Unicode. A simple and straightforward way that can store each Unicode code point, is to store each codepoint as two consecutive bytes. There are two possibilities: Store the bytes in big endian or in little endian order. These two encodings are called UTF-16-BE and UTF-16-LE respectively. Their disadvantage is that if e.g. you use UTF-16-BE on a little endian machine you will always have to swap bytes on encoding and decoding. UTF-16 avoids this problem: Bytes will always be in natural endianness. When these bytes are read by a CPU with a different endianness, then bytes have to be swapped though. To be able to detect the endianness of a UTF-16 byte sequence, there’s the so called BOM (the “Byte Order Mark”). This is the Unicode character U+FEFF. This character will be prepended to every UTF-16 byte sequence. The byte swapped version of this character (0xFFFE) is an illegal character that may not appear in a Unicode text. So when the first character in an UTF-16 byte sequence appears to be a U+FFFE the bytes have to be swapped on decoding. Unfortunately upto Unicode 4.0 the character U+FEFF had a second purpose as a ZERO WIDTH NO-BREAK SPACE: A character that has no width and doesn’t allow a word to be split. It can e.g. be used to give hints to a ligature algorithm. With Unicode 4.0 using U+FEFF as a ZERO WIDTH NO-BREAK SPACE has been deprecated (with U+2060 (WORD JOINER) assuming this role). Nevertheless Unicode software still must be able to handle U+FEFF in both roles: As a BOM it’s a device to determine the storage layout of the encoded bytes, and vanishes once the byte sequence has been decoded into a string; as a ZERO WIDTH NO-BREAK SPACE it’s a normal character that will be decoded like any other.
There’s another encoding that is able to encoding the full range of Unicode characters: UTF-8. UTF-8 is an 8-bit encoding, which means there are no issues with byte order in UTF-8. Each byte in a UTF-8 byte sequence consists of two parts: Marker bits (the most significant bits) and payload bits. The marker bits are a sequence of zero to six 1 bits followed by a 0 bit. Unicode characters are encoded like this (with x being payload bits, which when concatenated give the Unicode character):
| Range | Encoding |
|---|---|
| U-00000000 ... U-0000007F | 0xxxxxxx |
| U-00000080 ... U-000007FF | 110xxxxx 10xxxxxx |
| U-00000800 ... U-0000FFFF | 1110xxxx 10xxxxxx 10xxxxxx |
| U-00010000 ... U-001FFFFF | 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx |
| U-00200000 ... U-03FFFFFF | 111110xx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx |
| U-04000000 ... U-7FFFFFFF | 1111110x 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx 10xxxxxx |
The least significant bit of the Unicode character is the rightmost x bit.
As UTF-8 is an 8-bit encoding no BOM is required and any U+FEFF character in the decoded string (even if it’s the first character) is treated as a ZERO WIDTH NO-BREAK SPACE.
Without external information it’s impossible to reliably determine which encoding was used for encoding a string. Each charmap encoding can decode any random byte sequence. However that’s not possible with UTF-8, as UTF-8 byte sequences have a structure that doesn’t allow arbitrary byte sequences. To increase the reliability with which a UTF-8 encoding can be detected, Microsoft invented a variant of UTF-8 (that Python 2.5 calls "utf-8-sig") for its Notepad program: Before any of the Unicode characters is written to the file, a UTF-8 encoded BOM (which looks like this as a byte sequence: 0xef, 0xbb, 0xbf) is written. As it’s rather improbable that any charmap encoded file starts with these byte values (which would e.g. map to
LATIN SMALL LETTER I WITH DIAERESISRIGHT-POINTING DOUBLE ANGLE QUOTATION MARKINVERTED QUESTION MARK
in iso-8859-1), this increases the probability that a utf-8-sig encoding can be correctly guessed from the byte sequence. So here the BOM is not used to be able to determine the byte order used for generating the byte sequence, but as a signature that helps in guessing the encoding. On encoding the utf-8-sig codec will write 0xef, 0xbb, 0xbf as the first three bytes to the file. On decoding utf-8-sig will skip those three bytes if they appear as the first three bytes in the file.
Python comes with a number of codecs built-in, either implemented as C functions or with dictionaries as mapping tables. The following table lists the codecs by name, together with a few common aliases, and the languages for which the encoding is likely used. Neither the list of aliases nor the list of languages is meant to be exhaustive. Notice that spelling alternatives that only differ in case or use a hyphen instead of an underscore are also valid aliases.
Many of the character sets support the same languages. They vary in individual characters (e.g. whether the EURO SIGN is supported or not), and in the assignment of characters to code positions. For the European languages in particular, the following variants typically exist:
| Codec | Aliases | Languages |
|---|---|---|
| ascii | 646, us-ascii | English |
| big5 | big5-tw, csbig5 | Traditional Chinese |
| big5hkscs | big5-hkscs, hkscs | Traditional Chinese |
| cp037 | IBM037, IBM039 | English |
| cp424 | EBCDIC-CP-HE, IBM424 | Hebrew |
| cp437 | 437, IBM437 | English |
| cp500 | EBCDIC-CP-BE, EBCDIC-CP-CH, IBM500 | Western Europe |
| cp737 | Greek | |
| cp775 | IBM775 | Baltic languages |
| cp850 | 850, IBM850 | Western Europe |
| cp852 | 852, IBM852 | Central and Eastern Europe |
| cp855 | 855, IBM855 | Bulgarian, Byelorussian, Macedonian, Russian, Serbian |
| cp856 | Hebrew | |
| cp857 | 857, IBM857 | Turkish |
| cp860 | 860, IBM860 | Portuguese |
| cp861 | 861, CP-IS, IBM861 | Icelandic |
| cp862 | 862, IBM862 | Hebrew |
| cp863 | 863, IBM863 | Canadian |
| cp864 | IBM864 | Arabic |
| cp865 | 865, IBM865 | Danish, Norwegian |
| cp866 | 866, IBM866 | Russian |
| cp869 | 869, CP-GR, IBM869 | Greek |
| cp874 | Thai | |
| cp875 | Greek | |
| cp932 | 932, ms932, mskanji, ms-kanji | Japanese |
| cp949 | 949, ms949, uhc | Korean |
| cp950 | 950, ms950 | Traditional Chinese |
| cp1006 | Urdu | |
| cp1026 | ibm1026 | Turkish |
| cp1140 | ibm1140 | Western Europe |
| cp1250 | windows-1250 | Central and Eastern Europe |
| cp1251 | windows-1251 | Bulgarian, Byelorussian, Macedonian, Russian, Serbian |
| cp1252 | windows-1252 | Western Europe |
| cp1253 | windows-1253 | Greek |
| cp1254 | windows-1254 | Turkish |
| cp1255 | windows-1255 | Hebrew |
| cp1256 | windows1256 | Arabic |
| cp1257 | windows-1257 | Baltic languages |
| cp1258 | windows-1258 | Vietnamese |
| euc_jp | eucjp, ujis, u-jis | Japanese |
| euc_jis_2004 | jisx0213, eucjis2004 | Japanese |
| euc_jisx0213 | eucjisx0213 | Japanese |
| euc_kr | euckr, korean, ksc5601, ks_c-5601, ks_c-5601-1987, ksx1001, ks_x-1001 | Korean |
| gb2312 | chinese, csiso58gb231280, euc- cn, euccn, eucgb2312-cn, gb2312-1980, gb2312-80, iso- ir-58 | Simplified Chinese |
| gbk | 936, cp936, ms936 | Unified Chinese |
| gb18030 | gb18030-2000 | Unified Chinese |
| hz | hzgb, hz-gb, hz-gb-2312 | Simplified Chinese |
| iso2022_jp | csiso2022jp, iso2022jp, iso-2022-jp | Japanese |
| iso2022_jp_1 | iso2022jp-1, iso-2022-jp-1 | Japanese |
| iso2022_jp_2 | iso2022jp-2, iso-2022-jp-2 | Japanese, Korean, Simplified Chinese, Western Europe, Greek |
| iso2022_jp_2004 | iso2022jp-2004, iso-2022-jp-2004 | Japanese |
| iso2022_jp_3 | iso2022jp-3, iso-2022-jp-3 | Japanese |
| iso2022_jp_ext | iso2022jp-ext, iso-2022-jp-ext | Japanese |
| iso2022_kr | csiso2022kr, iso2022kr, iso-2022-kr | Korean |
| latin_1 | iso-8859-1, iso8859-1, 8859, cp819, latin, latin1, L1 | West Europe |
| iso8859_2 | iso-8859-2, latin2, L2 | Central and Eastern Europe |
| iso8859_3 | iso-8859-3, latin3, L3 | Esperanto, Maltese |
| iso8859_4 | iso-8859-4, latin4, L4 | Baltic languages |
| iso8859_5 | iso-8859-5, cyrillic | Bulgarian, Byelorussian, Macedonian, Russian, Serbian |
| iso8859_6 | iso-8859-6, arabic | Arabic |
| iso8859_7 | iso-8859-7, greek, greek8 | Greek |
| iso8859_8 | iso-8859-8, hebrew | Hebrew |
| iso8859_9 | iso-8859-9, latin5, L5 | Turkish |
| iso8859_10 | iso-8859-10, latin6, L6 | Nordic languages |
| iso8859_13 | iso-8859-13 | Baltic languages |
| iso8859_14 | iso-8859-14, latin8, L8 | Celtic languages |
| iso8859_15 | iso-8859-15 | Western Europe |
| johab | cp1361, ms1361 | Korean |
| koi8_r | Russian | |
| koi8_u | Ukrainian | |
| mac_cyrillic | maccyrillic | Bulgarian, Byelorussian, Macedonian, Russian, Serbian |
| mac_greek | macgreek | Greek |
| mac_iceland | maciceland | Icelandic |
| mac_latin2 | maclatin2, maccentraleurope | Central and Eastern Europe |
| mac_roman | macroman | Western Europe |
| mac_turkish | macturkish | Turkish |
| ptcp154 | csptcp154, pt154, cp154, cyrillic-asian | Kazakh |
| shift_jis | csshiftjis, shiftjis, sjis, s_jis | Japanese |
| shift_jis_2004 | shiftjis2004, sjis_2004, sjis2004 | Japanese |
| shift_jisx0213 | shiftjisx0213, sjisx0213, s_jisx0213 | Japanese |
| utf_32 | U32, utf32 | all languages |
| utf_32_be | UTF-32BE | all languages |
| utf_32_le | UTF-32LE | all languages |
| utf_16 | U16, utf16 | all languages |
| utf_16_be | UTF-16BE | all languages (BMP only) |
| utf_16_le | UTF-16LE | all languages (BMP only) |
| utf_7 | U7, unicode-1-1-utf-7 | all languages |
| utf_8 | U8, UTF, utf8 | all languages |
| utf_8_sig | all languages |
| Codec | Aliases | Purpose |
|---|---|---|
| idna | Implements RFC 3490, see also encodings.idna | |
| mbcs | dbcs | Windows only: Encode operand according to the ANSI codepage (CP_ACP) |
| palmos | Encoding of PalmOS 3.5 | |
| punycode | Implements RFC 3492 | |
| raw_unicode_escape | Produce a string that is suitable as raw Unicode literal in Python source code | |
| undefined | Raise an exception for all conversions. Can be used as the system encoding if no automatic coercion between byte and Unicode strings is desired. | |
| unicode_escape | Produce a string that is suitable as Unicode literal in Python source code | |
| unicode_internal | Return the internal representation of the operand |
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 http.client and ftplib, accept Unicode host names (http.client 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.
This module implements a variant of the UTF-8 codec: On encoding a UTF-8 encoded BOM will be prepended to the UTF-8 encoded bytes. For the stateful encoder this is only done once (on the first write to the byte stream). For decoding an optional UTF-8 encoded BOM at the start of the data will be skipped.
