This module defines base classes for standard Python codecs (encoders anddecoders) and provides access to the internal Python codec registry whichmanages the codec and error handling lookup process.
It defines the following functions:
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Encodes obj using the codec registered for encoding.
Errors may be given to set the desired error handling scheme. Thedefault error handler is strict meaning that encoding errors raiseValueError (or a more codec specific subclass, such asUnicodeEncodeError). Refer to Codec Base Classes for moreinformation on codec error handling.
Decodes obj using the codec registered for encoding.
Errors may be given to set the desired error handling scheme. Thedefault error handler is strict meaning that decoding errors raiseValueError (or a more codec specific subclass, such asUnicodeDecodeError). Refer to Codec Base Classes for moreinformation on codec error handling.
Register a codec search function. Search functions are expected to take oneargument, the encoding name in all lower case letters, and return aCodecInfo object having the following attributes:
- name The name of the encoding;
- encode The stateless encoding function;
- decode The stateless decoding function;
- incrementalencoder An incremental encoder class or factory function;
- incrementaldecoder An incremental decoder class or factory function;
- streamwriter A stream writer class or factory function;
- streamreader A stream reader class or factory function.
The various functions or classes take the following arguments:
encode and decode: These must be functions or methods which have the sameinterface as the encode()/decode() methods of Codecinstances (see Codec Interface). The functions/methodsare expected to work in a stateless mode.
incrementalencoder and incrementaldecoder: These have to be factoryfunctions providing the following interface:
The factory functions must return objects providing the interfaces defined bythe base classes IncrementalEncoder and IncrementalDecoder,respectively. Incremental codecs can maintain state.
streamreader and streamwriter: These have to be factory functions providingthe following interface:
The factory functions must return objects providing the interfaces defined bythe base classes StreamReader and StreamWriter, 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 '?' or 'ufffd'
- 'ignore': ignore malformed data and continue without further notice
- 'xmlcharrefreplace': replace with the appropriate XML characterreference (for encoding only)
- 'backslashreplace': replace with backslashed escape sequences (forencoding only)
- 'surrogateescape': on decoding, replace with code points in the UnicodePrivate Use Area ranging from U+DC80 to U+DCFF. These private codepoints will then be turned back into the same bytes when thesurrogateescape error handler is used when encoding the data.(See PEP 383 for more.)
as well as any other error handling name defined via register_error().
In case a search function cannot find a given encoding, it should returnNone.
Looks up the codec info in the Python codec registry and returns aCodecInfo object as defined above.
Encodings are first looked up in the registry’s cache. If not found, the list ofregistered search functions is scanned. If no CodecInfo object isfound, a LookupError is raised. Otherwise, the CodecInfo objectis stored in the cache and returned to the caller.
To simplify access to the various codecs, the module provides these additionalfunctions 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 encoderclass or factory function.
Raises a LookupError in case the encoding cannot be found or the codecdoesn’t support an incremental encoder.
Look up the codec for the given encoding and return its incremental decoderclass or factory function.
Raises a LookupError in case the encoding cannot be found or the codecdoesn’t support an incremental decoder.
Look up the codec for the given encoding and return its StreamReader class orfactory function.
Raises a LookupError in case the encoding cannot be found.
Look up the codec for the given encoding and return its StreamWriter class orfactory 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 UnicodeEncodeErrorinstance, which contains information about the location of the error. Theerror handler must either raise this or a different exception or return atuple with a replacement for the unencodable part of the input and a positionwhere encoding should continue. The replacement may be either str orbytes. If the replacement is bytes, the encoder will simply copythem into the output buffer. If the replacement is a string, the encoder willencode the replacement. Encoding continues on original input at thespecified position. Negative position values will be treated as beingrelative to the end of the input string. If the resulting position is out ofbound an IndexError will be raised.
Decoding and translating works similar, except UnicodeDecodeError orUnicodeTranslateError will be passed to the handler and that thereplacement 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.
Implements the strict error handling: each encoding or decoding errorraises a UnicodeError.
Implements the replace error handling: malformed data is replaced with asuitable replacement character such as '?' in bytestrings and'ufffd' in Unicode strings.
Implements the ignore error handling: malformed data is ignored andencoding or decoding is continued without further notice.
Implements the xmlcharrefreplace error handling (for encoding only): theunencodable character is replaced by an appropriate XML character reference.
Implements the backslashreplace error handling (for encoding only): theunencodable character is replaced by a backslashed escape sequence.
To simplify working with encoded files or stream, the module also defines theseutility functions:
Open an encoded file using the given mode and return a wrapped versionproviding 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. Bytesarguments will be rejected.
Note
Files are always opened in binary mode, even if no binary mode wasspecified. This is done to avoid data loss due to encodings using 8-bitvalues. This means that no automatic conversion of b'n' is doneon 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. Itdefaults to line buffered.
Return a wrapped version of file which provides transparent encodingtranslation.
Bytes written to the wrapped file are interpreted according to the givendata_encoding and then written to the original file as bytes using thefile_encoding.
If file_encoding is not given, it defaults to data_encoding.
errors may be given to define the error handling. It defaults to'strict', which causes ValueError to be raised in case an encodingerror occurs.
Uses an incremental encoder to iteratively encode the input provided byiterator. This function is a generator. errors (as well as anyother keyword argument) is passed through to the incremental encoder.
Uses an incremental decoder to iteratively decode the input provided byiterator. This function is a generator. errors (as well as anyother keyword argument) is passed through to the incremental decoder.
The module also provides the following constants which are useful for readingand writing to platform dependent files:
These constants define various encodings of the Unicode byte order mark (BOM)used in UTF-16 and UTF-32 data streams to indicate the byte order used in thestream or file and in UTF-8 as a Unicode signature. BOM_UTF16 is eitherBOM_UTF16_BE or BOM_UTF16_LE depending on the platform’snative byte order, BOM is an alias for BOM_UTF16,BOM_LE for BOM_UTF16_LE and BOM_BE forBOM_UTF16_BE. The others represent the BOM in UTF-8 and UTF-32encodings.
7.2.1. Codec Base Classes¶
The codecs module defines a set of base classes which define theinterface and can also be used to easily write your own codecs for use inPython.
Each codec has to define four interfaces to make it usable as codec in Python:stateless encoder, stateless decoder, stream reader and stream writer. Thestream reader and writers typically reuse the stateless encoder/decoder toimplement the file protocols.
The Codec class defines the interface for stateless encoders/decoders.
To simplify and standardize error handling, the encode() anddecode() methods may implement different error handling schemes byproviding the errors string argument. The following string values are definedand 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 thenext. |
| 'replace' | Replace with a suitable replacementcharacter; Python will use the officialU+FFFD REPLACEMENT CHARACTER for the built-inUnicode codecs on decoding and ‘?’ onencoding. |
| 'xmlcharrefreplace' | Replace with the appropriate XML characterreference (only for encoding). |
| 'backslashreplace' | Replace with backslashed escape sequences(only for encoding). |
| 'surrogateescape' | Replace byte with surrogate U+DCxx, as definedin PEP 383. |
In addition, the following error handlers are specific to a single codec:
| Value | Codec | Meaning |
|---|---|---|
| 'surrogatepass' | utf-8 | Allow encoding and decoding of surrogatecodes in UTF-8. |
New in version 3.1: The 'surrogateescape' and 'surrogatepass' error handlers.
The set of allowed values can be extended via register_error().
7.2.1.1. Codec Objects¶
The Codec class defines these methods which also define the functioninterfaces 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 particularcharacter 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. UseStreamCodec for codecs which have to keep state in order to makeencoding/decoding efficient.
The encoder must be able to handle zero length input and return an empty objectof the output object type in this situation.
Decodes the object input and returns a tuple (output object, lengthconsumed). Decoding converts a bytes object encoded using a particularcharacter set encoding to a string object.
input must be a bytes object or one which provides the read-only characterbuffer 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. UseStreamCodec for codecs which have to keep state in order to makeencoding/decoding efficient.
The decoder must be able to handle zero length input and return an empty objectof the output object type in this situation.
The IncrementalEncoder and IncrementalDecoder classes providethe basic interface for incremental encoding and decoding. Encoding/decoding theinput isn’t done with one call to the stateless encoder/decoder function, butwith multiple calls to theencode()/decode() method ofthe incremental encoder/decoder. The incremental encoder/decoder keeps track ofthe encoding/decoding process during method calls.
The joined output of calls to theencode()/decode() method isthe same as if all the single inputs were joined into one, and this input wasencoded/decoded with the stateless encoder/decoder.
7.2.1.2. IncrementalEncoder Objects¶
The IncrementalEncoder class is used for encoding an input in multiplesteps. It defines the following methods which every incremental encoder mustdefine 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 freeto add additional keyword arguments, but only the ones defined here are used bythe Python codec registry.
The IncrementalEncoder may implement different error handling schemesby providing the errors keyword argument. These parameters are predefined:
- 'strict' Raise ValueError (or a subclass); this is the default.
- 'ignore' Ignore the character and continue with the next.
- 'replace' Replace with a suitable replacement character
- 'xmlcharrefreplace' Replace with the appropriate XML character reference
- 'backslashreplace' Replace with backslashed escape sequences.
The errors argument will be assigned to an attribute of the same name.Assigning to this attribute makes it possible to switch between different errorhandling strategies during the lifetime of the IncrementalEncoderobject.
The set of allowed values for the errors argument can be extended withregister_error().
Encodes object (taking the current state of the encoder into account)and returns the resulting encoded object. If this is the last call toencode()final must be true (the default is false).
Reset the encoder to the initial state. The output is discarded: call.encode(',final=True) to reset the encoder and to get the output.
Return the current state of the encoder which must be an integer. Theimplementation should make sure that 0 is the most common state. (Statesthat are more complicated than integers can be converted into an integer bymarshaling/pickling the state and encoding the bytes of the resulting stringinto an integer).
Set the state of the encoder to state. state must be an encoder statereturned by getstate().
7.2.1.3. IncrementalDecoder Objects¶
The IncrementalDecoder class is used for decoding an input in multiplesteps. It defines the following methods which every incremental decoder mustdefine 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 freeto add additional keyword arguments, but only the ones defined here are used bythe Python codec registry.
The IncrementalDecoder may implement different error handling schemesby providing the errors keyword argument. These parameters are predefined:
- 'strict' Raise ValueError (or a subclass); this is the default.
- 'ignore' Ignore the character and continue with the next.
- 'replace' Replace with a suitable replacement character.
The errors argument will be assigned to an attribute of the same name.Assigning to this attribute makes it possible to switch between different errorhandling strategies during the lifetime of the IncrementalDecoderobject.
The set of allowed values for the errors argument can be extended withregister_error().
Decodes object (taking the current state of the decoder into account)and returns the resulting decoded object. If this is the last call todecode()final must be true (the default is false). If final istrue the decoder must decode the input completely and must flush allbuffers. If this isn’t possible (e.g. because of incomplete byte sequencesat the end of the input) it must initiate error handling just like in thestateless case (which might raise an exception).
Reset the decoder to the initial state.
Return the current state of the decoder. This must be a tuple with twoitems, the first must be the buffer containing the still undecodedinput. The second must be an integer and can be additional stateinfo. (The implementation should make sure that 0 is the most commonadditional state info.) If this additional state info is 0 it must bepossible to set the decoder to the state which has no input buffered and0 as the additional state info, so that feeding the previouslybuffered input to the decoder returns it to the previous state withoutproducing any output. (Additional state info that is more complicated thanintegers can be converted into an integer by marshaling/pickling the infoand encoding the bytes of the resulting string into an integer.)
Set the state of the encoder to state. state must be a decoder statereturned by getstate().
The StreamWriter and StreamReader classes provide genericworking interfaces which can be used to implement new encoding submodules veryeasily. See encodings.utf_8 for an example of how this is done.
7.2.1.4. StreamWriter Objects¶
The StreamWriter class is a subclass of Codec and defines thefollowing methods which every stream writer must define in order to becompatible with the Python codec registry.
Constructor for a StreamWriter instance.
All stream writers must provide this constructor interface. They are free to addadditional keyword arguments, but only the ones defined here are used by thePython codec registry.
stream must be a file-like object open for writing binary data.
The StreamWriter may implement different error handling schemes byproviding the errors keyword argument. These parameters are predefined:
- 'strict' Raise ValueError (or a subclass); this is the default.
- 'ignore' Ignore the character and continue with the next.
- 'replace' Replace with a suitable replacement character
- 'xmlcharrefreplace' Replace with the appropriate XML character reference
- 'backslashreplace' Replace with backslashed escape sequences.
The errors argument will be assigned to an attribute of the same name.Assigning to this attribute makes it possible to switch between different errorhandling strategies during the lifetime of the StreamWriter object.
The set of allowed values for the errors argument can be extended withregister_error().
Writes the object’s contents encoded to the stream.
Writes the concatenated list of strings to the stream (possibly by reusingthe write() method).
Flushes and resets the codec buffers used for keeping state.
Calling this method should ensure that the data on the output is put intoa clean state that allows appending of new fresh data without having torescan the whole stream to recover state.
In addition to the above methods, the StreamWriter must also inheritall other methods and attributes from the underlying stream.
7.2.1.5. StreamReader Objects¶
The StreamReader class is a subclass of Codec and defines thefollowing methods which every stream reader must define in order to becompatible with the Python codec registry.
Constructor for a StreamReader instance.
All stream readers must provide this constructor interface. They are free to addadditional keyword arguments, but only the ones defined here are used by thePython codec registry.
stream must be a file-like object open for reading (binary) data.
The StreamReader may implement different error handling schemes byproviding the errors keyword argument. These parameters are defined:
- 'strict' Raise ValueError (or a subclass); this is the default.
- 'ignore' Ignore the character and continue with the next.
- 'replace' Replace with a suitable replacement character.
The errors argument will be assigned to an attribute of the same name.Assigning to this attribute makes it possible to switch between different errorhandling strategies during the lifetime of the StreamReader object.
The set of allowed values for the errors argument can be extended withregister_error().
Decodes data from the stream and returns the resulting object.
chars indicates the number of characters to read from thestream. read() will never return more than chars characters, butit might return less, if there are not enough characters available.
size indicates the approximate maximum number of bytes to read from thestream for decoding purposes. The decoder can modify this setting asappropriate. The default value -1 indicates to read and decode as much aspossible. size is intended to prevent having to decode huge files inone step.
firstline indicates that it would be sufficient to only return the firstline, if there are decoding errors on later lines.
The method should use a greedy read strategy meaning that it should readas much data as is allowed within the definition of the encoding and thegiven size, e.g. if optional encoding endings or state markers areavailable 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’sread() method.
If keepends is false line-endings will be stripped from the linesreturned.
Read all lines available on the input stream and return them as a list oflines.
Line-endings are implemented using the codec’s decoder method and areincluded in the list entries if keepends is true.
sizehint, if given, is passed as the size argument to the stream’sread() method.
Resets the codec buffers used for keeping state.
Note that no stream repositioning should take place. This method isprimarily intended to be able to recover from decoding errors.
In addition to the above methods, the StreamReader must also inheritall other methods and attributes from the underlying stream.
The next two base classes are included for convenience. They are not needed bythe codec registry, but may provide useful in practice.
7.2.1.6. StreamReaderWriter Objects¶
The StreamReaderWriter allows wrapping streams which work in both readand write modes.
Python Codecs Encoding
The design is such that one can use the factory functions returned by thelookup() function to construct the instance.
Creates a StreamReaderWriter instance. stream must be a file-likeobject. Reader and Writer must be factory functions or classes providing theStreamReader and StreamWriter interface resp. Error handlingis done in the same way as defined for the stream readers and writers.
StreamReaderWriter instances define the combined interfaces ofStreamReader and StreamWriter classes. They inherit all othermethods and attributes from the underlying stream.
7.2.1.7. StreamRecoder Objects¶
The StreamRecoder provide a frontend - backend view of encoding datawhich is sometimes useful when dealing with different encoding environments.
The design is such that one can use the factory functions returned by thelookup() 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 outputof write()) while Reader and Writer work on the backend (reading andwriting to the stream).
You can use these objects to do transparent direct recodings from e.g. Latin-1to 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 theStreamReader and StreamWriter interface respectively.
encode and decode are needed for the frontend translation, Reader andWriter for the backend translation.
Error handling is done in the same way as defined for the stream readers andwriters.
StreamRecoder instances define the combined interfaces ofStreamReader and StreamWriter classes. They inherit all othermethods and attributes from the underlying stream.
7.2.2. Encodings and Unicode¶
Strings are stored internally as sequences of codepoints in range 0-10FFFF(see PEP 393 for more details about the implementation).Once a string object is used outside of CPU and memory, CPU endiannessand how these arrays are stored as bytes become an issue. Transforming astring object into a sequence of bytes is called encoding and recreating thestring object from the sequence of bytes is known as decoding. There are manydifferent methods for how this transformation can be done (these methods arealso called encodings). The simplest method is to map the codepoints 0-255 tothe bytes 0x0-0xff. This means that a string object that containscodepoints above U+00FF can’t be encoded with this method (which is called'latin-1' or 'iso-8859-1'). str.encode() will raise aUnicodeEncodeError that looks like this: UnicodeEncodeError:'latin-1'codeccan'tencodecharacter'u1234'inposition3:ordinalnotinrange(256).
There’s another group of encodings (the so called charmap encodings) that choosea different subset of all Unicode code points and how these codepoints aremapped to the bytes 0x0-0xff. To see how this is done simply opene.g. encodings/cp1252.py (which is an encoding that is used primarily onWindows). There’s a string constant with 256 characters that shows you whichcharacter is mapped to which byte value.
All of these encodings can only encode 256 of the 1114112 codepointsdefined in Unicode. A simple and straightforward way that can store each Unicodecode point, is to store each codepoint as four consecutive bytes. There are twopossibilities: store the bytes in big endian or in little endian order. Thesetwo encodings are called UTF-32-BE and UTF-32-LE respectively. Theirdisadvantage is that if e.g. you use UTF-32-BE on a little endian machine youwill always have to swap bytes on encoding and decoding. UTF-32 avoids thisproblem: bytes will always be in natural endianness. When these bytes are readby a CPU with a different endianness, then bytes have to be swapped though. Tobe able to detect the endianness of a UTF-16 or UTF-32 byte sequence,there’s the so called BOM (“Byte Order Mark”). This is the Unicode characterU+FEFF. This character can be prepended to every UTF-16 or UTF-32byte sequence. The byte swapped version of this character (0xFFFE) is anillegal character that may not appear in a Unicode text. So when thefirst character in an UTF-16 or UTF-32 byte sequenceappears to be a U+FFFE the bytes have to be swapped on decoding.Unfortunately the character U+FEFF had a second purpose asa ZEROWIDTHNO-BREAKSPACE: a character that has no width and doesn’t allowa 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 ZEROWIDTHNO-BREAKSPACE has beendeprecated (with U+2060 (WORDJOINER) assuming this role). NeverthelessUnicode software still must be able to handle U+FEFF in both roles: as a BOMit’s a device to determine the storage layout of the encoded bytes, and vanishesonce the byte sequence has been decoded into a string; as a ZEROWIDTHNO-BREAKSPACE 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 Unicodecharacters: UTF-8. UTF-8 is an 8-bit encoding, which means there are no issueswith byte order in UTF-8. Each byte in a UTF-8 byte sequence consists of twoparts: marker bits (the most significant bits) and payload bits. The marker bitsare a sequence of zero to four 1 bits followed by a 0 bit. Unicode characters areencoded like this (with x being payload bits, which when concatenated give theUnicode character):
| Range | Encoding |
|---|---|
| U-00000000 ... U-0000007F | 0xxxxxxx |
| U-00000080 ... U-000007FF | 110xxxxx 10xxxxxx |
| U-00000800 ... U-0000FFFF | 1110xxxx 10xxxxxx 10xxxxxx |
| U-00010000 ... U-0010FFFF | 11110xxx 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 inthe decoded string (even if it’s the first character) is treated as a ZEROWIDTHNO-BREAKSPACE.
Without external information it’s impossible to reliably determine whichencoding was used for encoding a string. Each charmap encoding candecode any random byte sequence. However that’s not possible with UTF-8, asUTF-8 byte sequences have a structure that doesn’t allow arbitrary bytesequences. To increase the reliability with which a UTF-8 encoding can bedetected, Microsoft invented a variant of UTF-8 (that Python 2.5 calls'utf-8-sig') for its Notepad program: Before any of the Unicode charactersis written to the file, a UTF-8 encoded BOM (which looks like this as a bytesequence: 0xef, 0xbb, 0xbf) is written. As it’s rather improbablethat any charmap encoded file starts with these byte values (which would e.g.map to
in iso-8859-1), this increases the probability that a utf-8-sig encoding can becorrectly guessed from the byte sequence. So here the BOM is not used to be ableto determine the byte order used for generating the byte sequence, but as asignature that helps in guessing the encoding. On encoding the utf-8-sig codecwill write 0xef, 0xbb, 0xbf as the first three bytes to the file. Ondecoding utf-8-sig will skip those three bytes if they appear as the firstthree bytes in the file. In UTF-8, the use of the BOM is discouraged andshould generally be avoided.
7.2.3. Standard Encodings¶
Python comes with a number of codecs built-in, either implemented as C functionsor with dictionaries as mapping tables. The following table lists the codecs byname, together with a few common aliases, and the languages for which theencoding is likely used. Neither the list of aliases nor the list of languagesis meant to be exhaustive. Notice that spelling alternatives that only differ incase or use a hyphen instead of an underscore are also valid aliases; therefore,e.g. 'utf-8' is a valid alias for the 'utf_8' codec.
CPython implementation detail: Some common encodings can bypass the codecs lookup machinery toimprove performance. These optimization opportunities are onlyrecognized by CPython for a limited set of aliases: utf-8, utf8,latin-1, latin1, iso-8859-1, mbcs (Windows only), ascii, utf-16,and utf-32. Using alternative spellings for these encodings mayresult in slower execution.
Many of the character sets support the same languages. They vary in individualcharacters (e.g. whether the EURO SIGN is supported or not), and in theassignment of characters to code positions. For the European languages inparticular, the following variants typically exist:
- an ISO 8859 codeset
- a Microsoft Windows code page, which is typically derived from a 8859 codeset,but replaces control characters with additional graphic characters
- an IBM EBCDIC code page
- an IBM PC code page, which is ASCII compatible
| 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 |
| cp720 | Arabic | |
| 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 |
| cp858 | 858, IBM858 | Western Europe |
| 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 | windows-1256 | Arabic |
| cp1257 | windows-1257 | Baltic languages |
| cp1258 | windows-1258 | Vietnamese |
| cp65001 | Windows only: Windows UTF-8(CP_UTF8) | |
| 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, SimplifiedChinese, 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, latin7, L7 | Baltic languages |
| iso8859_14 | iso-8859-14, latin8, L8 | Celtic languages |
| iso8859_15 | iso-8859-15, latin9, L9 | Western Europe |
| iso8859_16 | iso-8859-16, latin10, L10 | South-Eastern 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, macintosh | 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 |
| utf_16_le | UTF-16LE | all languages |
| utf_7 | U7, unicode-1-1-utf-7 | all languages |
| utf_8 | U8, UTF, utf8 | all languages |
| utf_8_sig | all languages |
7.2.4. Python Specific Encodings¶
A number of predefined codecs are specific to Python, so their codec names haveno meaning outside Python. These are listed in the tables below based on theexpected input and output types (note that while text encodings are the mostcommon use case for codecs, the underlying codec infrastructure supportsarbitrary data transforms rather than just text encodings). For asymmetriccodecs, the stated purpose describes the encoding direction.
The following codecs provide str to bytes encoding andbytes-like object to str decoding, similar to the Unicode textencodings.
| Codec | Aliases | Purpose |
|---|---|---|
| idna | Implements RFC 3490,see alsoencodings.idna | |
| mbcs | dbcs | Windows only: Encodeoperand according to theANSI codepage (CP_ACP) |
| palmos | Encoding of PalmOS 3.5 | |
| punycode | Implements RFC 3492 | |
| raw_unicode_escape | Produce a string that issuitable as raw Unicodeliteral in Python sourcecode | |
| undefined | Raise an exception forall conversions. Can beused as the systemencoding if no automaticcoercion between byte andUnicode strings isdesired. | |
| unicode_escape | Produce a string that issuitable as Unicodeliteral in Python sourcecode | |
| unicode_internal | Return the internalrepresentation of theoperand |
The following codecs provide bytes-like object to bytesmappings.
| Codec | Purpose | Encoder/decoder |
|---|---|---|
| base64_codec [1] | Convert operand to MIMEbase64 (the result alwaysincludes a trailing'n') | base64.b64encode(),base64.b64decode() |
| bz2_codec | Compress the operandusing bz2 | bz2.compress(),bz2.decompress() |
| hex_codec | Convert operand tohexadecimalrepresentation, with twodigits per byte | base64.b16encode(),base64.b16decode() |
| quopri_codec | Convert operand to MIMEquoted printable | quopri.encodestring(),quopri.decodestring() |
| uu_codec | Convert the operand usinguuencode | uu.encode(),uu.decode() |
| zlib_codec | Compress the operandusing gzip | zlib.compress(),zlib.decompress() |
| [1] | Rather than accepting any bytes-like object,'base64_codec' accepts only bytes and bytearray forencoding and only bytes, bytearray, and ASCII-onlyinstances of str for decoding |
The following codecs provide str to str mappings.
| Codec | Purpose |
|---|---|
| rot_13 | Returns the Caesar-cypherencryption of the operand |
New in version 3.2: bytes-to-bytes and str-to-str codecs.
7.2.5. encodings.idna — Internationalized Domain Names in Applications¶
This module implements RFC 3490 (Internationalized Domain Names inApplications) and RFC 3492 (Nameprep: A Stringprep Profile forInternationalized Domain Names (IDN)). It builds upon the punycode encodingand stringprep.
These RFCs together define a protocol to support non-ASCII characters in domainnames. A domain name containing non-ASCII characters (such aswww.Alliancefrançaise.nu) is converted into an ASCII-compatible encoding(ACE, such as www.xn--alliancefranaise-npb.nu). The ACE form of the domainname is then used in all places where arbitrary characters are not allowed bythe protocol, such as DNS queries, HTTP Host fields, and soon. This conversion is carried out in the application; if possible invisible tothe user: The application should transparently convert Unicode domain labels toIDNA on the wire, and convert back ACE labels to Unicode before presenting themto the user.
Python supports this conversion in several ways: the idna codec performsconversion between Unicode and ACE, separating an input string into labelsbased on the separator characters defined in section 3.1 (1) of RFC 3490and converting each label to ACE as required, and conversely separating an inputbyte string into labels based on the . separator and converting any ACElabels found into unicode. Furthermore, the socket moduletransparently converts Unicode host names to ACE, so that applications need notbe concerned about converting host names themselves when they pass them to thesocket module. On top of that, modules that have host names as functionparameters, such as http.client and ftplib, accept Unicode hostnames (http.client then also transparently sends an IDNA hostname in theHost field if it sends that field at all).
When receiving host names from the wire (such as in reverse name lookup), noautomatic conversion to Unicode is performed: Applications wishing to presentsuch host names to the user should decode them to Unicode.
The module encodings.idna also implements the nameprep procedure, whichperforms certain normalizations on host names, to achieve case-insensitivity ofinternational domain names, and to unify similar characters. The nameprepfunctions can be used directly if desired.
Return the nameprepped version of label. The implementation currently assumesquery strings, so AllowUnassigned is true.
Convert a label to ASCII, as specified in RFC 3490. UseSTD3ASCIIRules isassumed to be false.
Convert a label to Unicode, as specified in RFC 3490.
7.2.6. encodings.mbcs — Windows ANSI codepage¶
Encode operand according to the ANSI codepage (CP_ACP).
Python Video Codec
Availability: Windows only.
Python Codecs Open File Example
Changed in version 3.3: Support any error handler.
Changed in version 3.2: Before 3.2, the errors argument was ignored; 'replace' was always usedto encode, and 'ignore' to decode.
7.2.7. encodings.utf_8_sig — UTF-8 codec with BOM signature¶
With Open Python Example
This module implements a variant of the UTF-8 codec: On encoding a UTF-8 encodedBOM will be prepended to the UTF-8 encoded bytes. For the stateful encoder thisis only done once (on the first write to the byte stream). For decoding anoptional UTF-8 encoded BOM at the start of the data will be skipped.