codecs â Codec registry and base classes¶
Source code: Lib/codecs.py
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. Most standard codecs are text encodings, which encode text to bytes (and decode bytes to text), but there are also codecs provided that encode text to text, and bytes to bytes. Custom codecs may encode and decode between arbitrary types, but some module features are restricted to be used specifically with text encodings or with codecs that encode to bytes.
The module defines the following functions for encoding and decoding with any codec:
Encodes obj using the codec registered for encoding.
Errors may be given to set the desired error handling scheme. The default error handler is 'strict' meaning that encoding errors raise ValueError (or a more codec specific subclass, such as UnicodeEncodeError). Refer to Codec Base Classes for more information on codec error handling.
Decodes obj using the codec registered for encoding.
Errors may be given to set the desired error handling scheme. The default error handler is 'strict' meaning that decoding errors raise ValueError (or a more codec specific subclass, such as UnicodeDecodeError). Refer to Codec Base Classes for more information on codec error handling.
The full details for each codec can also be looked up directly:
Looks up the codec info in the Python codec registry and returns a CodecInfo object as defined below.
Encodings are first looked up in the registryâs 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.
Codec details when looking up the codec registry. The constructor arguments are stored in attributes of the same name:
The name of the encoding.
The stateless encoding and decoding functions. These must be functions or methods which have the same interface as the encode() and decode() methods of Codec instances (see Codec Interface). The functions or methods are expected to work in a stateless mode.
Incremental encoder and decoder classes or factory functions. These have to provide the interface defined by the base classes IncrementalEncoder and IncrementalDecoder, respectively. Incremental codecs can maintain state.
Stream writer and reader classes or factory functions. These have to provide the interface defined by the base classes StreamWriter and StreamReader, respectively. Stream codecs can maintain state.
To simplify access to the various codec components, 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 doesnât 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 doesnât 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.
Custom codecs are made available by registering a suitable codec search function:
Register a codec search function. Search functions are expected to take one argument, being the encoding name in all lower case letters with hyphens and spaces converted to underscores, and return a CodecInfo object. In case a search function cannot find a given encoding, it should return None.
Changed in version 3.9: Hyphens and spaces are converted to underscore.
Unregister a codec search function and clear the registryâs cache. If the search function is not registered, do nothing.
New in version 3.10.
While the builtin open() and the associated io module are the recommended approach for working with encoded text files, this module provides additional utility functions and classes that allow the use of a wider range of codecs when working with binary files:
Open an encoded file using the given mode and return an instance of StreamReaderWriter, providing transparent encoding/decoding. The default file mode is 'r', meaning to open the file in read mode.
Note
If encoding is not None, then the underlying encoded files are always opened in binary mode. No automatic conversion of '\n' is done on reading and writing. The mode argument may be any binary mode acceptable to the built-in open() function; the 'b' is automatically added.
encoding specifies the encoding which is to be used for the file. Any encoding that encodes to and decodes from bytes is allowed, and the data types supported by the file methods depend on the codec used.
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 -1 which means that the default buffer size will be used.
Changed in version 3.11: The 'U' mode has been removed.
Return a StreamRecoder instance, a wrapped version of file which provides transparent transcoding. The original file is closed when the wrapped version is closed.
Data written to the wrapped file is decoded according to the given data_encoding and then written to the original file as bytes using file_encoding. Bytes read from the original file are decoded according to file_encoding, and the result is encoded using data_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 encoding error occurs.
Uses an incremental encoder to iteratively encode the input provided by iterator. This function is a generator. The errors argument (as well as any other keyword argument) is passed through to the incremental encoder.
This function requires that the codec accept text str objects to encode. Therefore it does not support bytes-to-bytes encoders such as base64_codec.
Uses an incremental decoder to iteratively decode the input provided by iterator. This function is a generator. The errors argument (as well as any other keyword argument) is passed through to the incremental decoder.
This function requires that the codec accept bytes objects to decode. Therefore it does not support text-to-text encoders such as rot_13, although rot_13 may be used equivalently with iterencode().
The module also provides the following constants which are useful for reading and writing to platform dependent files:
These constants define various byte sequences, being Unicode byte order marks (BOMs) for several encodings. They are used in UTF-16 and UTF-32 data streams to indicate the byte order used, and in UTF-8 as a Unicode signature. BOM_UTF16 is either BOM_UTF16_BE or BOM_UTF16_LE depending on the platformâs native byte order, BOM is an alias for BOM_UTF16, BOM_LE for BOM_UTF16_LE and BOM_BE for BOM_UTF16_BE. The others represent the BOM in UTF-8 and UTF-32 encodings.
The codecs module defines a set of base classes which define the interfaces for working with codec objects, and can also be used as the basis for custom codec implementations.
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. Codec authors also need to define how the codec will handle encoding and decoding errors.
Error Handlers¶To simplify and standardize error handling, codecs may implement different error handling schemes by accepting the errors string argument:
>>> 'German Ã, â¬'.encode(encoding='ascii', errors='backslashreplace') b'German \\xdf, \\u266c' >>> 'German Ã, â¬'.encode(encoding='ascii', errors='xmlcharrefreplace') b'German ß, ♬'
The following error handlers can be used with all Python Standard Encodings codecs:
Value
Meaning
'strict'
Raise UnicodeError (or a subclass), this is the default. Implemented in strict_errors().
'ignore'
Ignore the malformed data and continue without further notice. Implemented in ignore_errors().
'replace'
Replace with a replacement marker. On encoding, use ? (ASCII character). On decoding, use � (U+FFFD, the official REPLACEMENT CHARACTER). Implemented in replace_errors().
'backslashreplace'
Replace with backslashed escape sequences. On encoding, use hexadecimal form of Unicode code point with formats \xhh \uxxxx \Uxxxxxxxx. On decoding, use hexadecimal form of byte value with format \xhh. Implemented in backslashreplace_errors().
'surrogateescape'
On decoding, replace byte with individual surrogate code ranging from U+DC80 to U+DCFF. This code will then be turned back into the same byte when the 'surrogateescape' error handler is used when encoding the data. (See PEP 383 for more.)
The following error handlers are only applicable to encoding (within text encodings):
Value
Meaning
'xmlcharrefreplace'
Replace with XML/HTML numeric character reference, which is a decimal form of Unicode code point with format &#num;. Implemented in xmlcharrefreplace_errors().
'namereplace'
Replace with \N{...} escape sequences, what appears in the braces is the Name property from Unicode Character Database. Implemented in namereplace_errors().
In addition, the following error handler is specific to the given codecs:
Value
Codecs
Meaning
'surrogatepass'
utf-8, utf-16, utf-32, utf-16-be, utf-16-le, utf-32-be, utf-32-le
Allow encoding and decoding surrogate code point (U+D800 - U+DFFF) as normal code point. Otherwise these codecs treat the presence of surrogate code point in str as an error.
New in version 3.1: The 'surrogateescape' and 'surrogatepass' error handlers.
Changed in version 3.4: The 'surrogatepass' error handler now works with utf-16* and utf-32* codecs.
New in version 3.5: The 'namereplace' error handler.
Changed in version 3.5: The 'backslashreplace' error handler now works with decoding and translating.
The set of allowed values can be extended by registering a new named error handler:
Register the error handling function error_handler under the name name. The error_handler argument 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 replacement may be either str or bytes. If the replacement is bytes, the encoder will simply copy them into the output buffer. If the replacement is a string, the encoder will encode the replacement. Encoding continues on 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 similarly, 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.
Previously registered error handlers (including the standard error handlers) can be looked up by name:
Return the error handler previously registered under the name name.
Raises a LookupError in case the handler cannot be found.
The following standard error handlers are also made available as module level functions:
Implements the 'strict' error handling.
Each encoding or decoding error raises a UnicodeError.
Implements the 'ignore' error handling.
Malformed data is ignored; encoding or decoding is continued without further notice.
Implements the 'replace' error handling.
Substitutes ? (ASCII character) for encoding errors or � (U+FFFD, the official REPLACEMENT CHARACTER) for decoding errors.
Implements the 'backslashreplace' error handling.
Malformed data is replaced by a backslashed escape sequence. On encoding, use the hexadecimal form of Unicode code point with formats \xhh \uxxxx \Uxxxxxxxx. On decoding, use the hexadecimal form of byte value with format \xhh.
Changed in version 3.5: Works with decoding and translating.
Implements the 'xmlcharrefreplace' error handling (for encoding within text encoding only).
The unencodable character is replaced by an appropriate XML/HTML numeric character reference, which is a decimal form of Unicode code point with format &#num; .
Implements the 'namereplace' error handling (for encoding within text encoding only).
The unencodable character is replaced by a \N{...} escape sequence. The set of characters that appear in the braces is the Name property from Unicode Character Database. For example, the German lowercase letter 'Ã' will be converted to byte sequence \N{LATIN SMALL LETTER SHARP S} .
New in version 3.5.
The base 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). For instance, text encoding converts a string object to a bytes object using a particular character set encoding (e.g., cp1252 or iso-8859-1).
The errors argument defines the error handling to apply. It defaults to 'strict' handling.
The method may not store state in the Codec instance. Use StreamWriter for codecs which have to keep state in order to make encoding 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). For instance, for a text encoding, decoding converts a bytes object encoded using a particular character set encoding to a string object.
For text encodings and bytes-to-bytes codecs, input must be a bytes object or one which provides the read-only buffer interface â for example, buffer objects and memory mapped files.
The errors argument defines the error handling to apply. It defaults to 'strict' handling.
The method may not store state in the Codec instance. Use StreamReader for codecs which have to keep state in order to make 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 isnât 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. See Error Handlers for possible values.
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.
Encodes object (taking the current state of the encoder into account) and returns the resulting encoded object. If this is the last call to encode() final must be true (the default is false).
Reset the encoder to the initial state. The output is discarded: call .encode(object, final=True), passing an empty byte or text string if necessary, to reset the encoder and to get the output.
Return the current state of the encoder which must be an integer. The implementation should make sure that 0 is the most common state. (States that are more complicated than integers can be converted into an integer by marshaling/pickling the state and encoding the bytes of the resulting string into an integer.)
Set the state of the encoder to state. state must be an encoder state returned by getstate().
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. See Error Handlers for possible values.
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.
Decodes object (taking the current state of the decoder into account) and returns the resulting decoded object. If this is the last call to decode() final must be true (the default is false). If final is true the decoder must decode the input completely and must flush all buffers. If this isnât possible (e.g. because of incomplete byte sequences at the end of the input) it must initiate error handling just like in the stateless 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 two items, the first must be the buffer containing the still undecoded input. The second must be an integer and can be additional state info. (The implementation should make sure that 0 is the most common additional state info.) If this additional state info is 0 it must be possible to set the decoder to the state which has no input buffered and 0 as the additional state info, so that feeding the previously buffered input to the decoder returns it to the previous state without producing any output. (Additional state info that is more complicated than integers can be converted into an integer by marshaling/pickling the info and encoding the bytes of the resulting string into an integer.)
Set the state of the decoder to state. state must be a decoder state returned by getstate().
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.
The stream argument must be a file-like object open for writing text or binary data, as appropriate for the specific codec.
The StreamWriter may implement different error handling schemes by providing the errors keyword argument. See Error Handlers for the standard error handlers the underlying stream codec may support.
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.
Writes the objectâs contents encoded to the stream.
Writes the concatenated iterable of strings to the stream (possibly by reusing the write() method). Infinite or very large iterables are not supported. The standard bytes-to-bytes codecs do not support this method.
Resets the codec buffers used for keeping internal 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.
The stream argument must be a file-like object open for reading text or binary data, as appropriate for the specific codec.
The StreamReader may implement different error handling schemes by providing the errors keyword argument. See Error Handlers for the standard error handlers the underlying stream codec may support.
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.
The chars argument indicates the number of decoded code points or bytes to return. The read() method will never return more data than requested, but it might return less, if there is not enough available.
The size argument indicates the approximate maximum number of encoded bytes or code points to read for decoding. The decoder can modify this setting as appropriate. The default value -1 indicates to read and decode as much as possible. This parameter is intended to prevent having to decode huge files in one step.
The firstline flag 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 streamâs read() 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 codecâs decode() method and are included in the list entries if keepends is true.
sizehint, if given, is passed as the size argument to the streamâs read() method.
Resets the codec buffers used for keeping internal 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 StreamReaderWriter is a convenience class that 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.
Creates a StreamReaderWriter instance. stream must be a file-like object. Reader and Writer must be factory functions or classes providing the StreamReader and StreamWriter interface resp. Error handling is done in the same way as defined for the stream readers and writers.
StreamReaderWriter instances define the combined interfaces of StreamReader and StreamWriter classes. They inherit all other methods and attributes from the underlying stream.
The StreamRecoder translates data from one encoding to another, 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 â the data visible to code calling read() and write(), while Reader and Writer work on the backend â the data in stream.
You can use these objects to do transparent transcodings, e.g., from Latin-1 to UTF-8 and back.
The stream argument must be a file-like object.
The encode and decode arguments must adhere to the Codec interface. Reader and Writer must be factory functions or classes providing objects of the StreamReader and StreamWriter interface respectively.
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 code points in range U+0000âU+10FFFF. (See PEP 393 for more details about the implementation.) Once a string object is used outside of CPU and memory, endianness and how these arrays are stored as bytes become an issue. As with other codecs, serialising a string into a sequence of bytes is known as encoding, and recreating the string from the sequence of bytes is known as decoding. There are a variety of different text serialisation codecs, which are collectivity referred to as text encodings.
The simplest text encoding (called 'latin-1' or 'iso-8859-1') maps the code points 0â255 to the bytes 0x0â0xff, which means that a string object that contains code points above U+00FF canât be encoded with this codec. Doing so will raise a UnicodeEncodeError that looks like the following (although the details of the error message may differ): UnicodeEncodeError: 'latin-1' codec can't encode character '\u1234' in position 3: ordinal not in range(256).
Thereâs another group of encodings (the so called charmap encodings) that choose a different subset of all Unicode code points and how these code points are mapped to the bytes 0x0â0xff. To see how this is done simply open e.g. encodings/cp1252.py (which is an encoding that is used primarily on Windows). Thereâs 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 1114112 code points defined in Unicode. A simple and straightforward way that can store each Unicode code point, is to store each code point as four consecutive bytes. There are two possibilities: store the bytes in big endian or in little endian order. These two encodings are called UTF-32-BE and UTF-32-LE respectively. Their disadvantage is that if e.g. you use UTF-32-BE on a little endian machine you will always have to swap bytes on encoding and decoding. UTF-32 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 or UTF-32 byte sequence, thereâs the so called BOM (âByte Order Markâ). This is the Unicode character U+FEFF. This character can be prepended to every UTF-16 or UTF-32 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 a UTF-16 or UTF-32 byte sequence appears to be a U+FFFE the bytes have to be swapped on decoding. Unfortunately the character U+FEFF had a second purpose as a ZERO WIDTH NO-BREAK SPACE: a character that has no width and doesnât 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 itâs 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 itâs a normal character that will be decoded like any other.
Thereâs another encoding that is able to encode 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 four 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-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 in the decoded string (even if itâs the first character) is treated as a ZERO WIDTH NO-BREAK SPACE.
Without external information itâs impossible to reliably determine which encoding was used for encoding a string. Each charmap encoding can decode any random byte sequence. However thatâs not possible with UTF-8, as UTF-8 byte sequences have a structure that doesnât 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 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 itâs rather improbable that any charmap encoded file starts with these byte values (which would e.g. map to
LATIN SMALL LETTER I WITH DIAERESIS
RIGHT-POINTING DOUBLE ANGLE QUOTATION MARK
INVERTED 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. In UTF-8, the use of the BOM is discouraged and should generally be avoided.
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; 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 to improve performance. These optimization opportunities are only recognized by CPython for a limited set of (case insensitive) aliases: utf-8, utf8, latin-1, latin1, iso-8859-1, iso8859-1, mbcs (Windows only), ascii, us-ascii, utf-16, utf16, utf-32, utf32, and the same using underscores instead of dashes. Using alternative aliases for these encodings may result in slower execution.
Changed in version 3.6: Optimization opportunity recognized for us-ascii.
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:
an ISO 8859 codeset
a Microsoft Windows code page, which is typically derived from an 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
cp273
273, IBM273, csIBM273
German
New in version 3.4.
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
cp1125
1125, ibm1125, cp866u, ruscii
Ukrainian
New in version 3.4.
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
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
Western 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_11
iso-8859-11, thai
Thai 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_t
Tajik
New in version 3.5.
koi8_u
Ukrainian
kz1048
kz_1048, strk1048_2002, rk1048
Kazakh
New in version 3.5.
mac_cyrillic
maccyrillic
Bulgarian, Byelorussian, Macedonian, Russian, Serbian
mac_greek
macgreek
Greek
mac_iceland
maciceland
Icelandic
mac_latin2
maclatin2, maccentraleurope, mac_centeuro
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, cp65001
all languages
utf_8_sig
all languages
Changed in version 3.4: The utf-16* and utf-32* encoders no longer allow surrogate code points (U+D800âU+DFFF) to be encoded. The utf-32* decoders no longer decode byte sequences that correspond to surrogate code points.
Changed in version 3.8: cp65001 is now an alias to utf_8.
A number of predefined codecs are specific to Python, so their codec names have no meaning outside Python. These are listed in the tables below based on the expected input and output types (note that while text encodings are the most common use case for codecs, the underlying codec infrastructure supports arbitrary data transforms rather than just text encodings). For asymmetric codecs, the stated meaning describes the encoding direction.
Text Encodings¶The following codecs provide str to bytes encoding and bytes-like object to str decoding, similar to the Unicode text encodings.
Codec
Aliases
Meaning
idna
Implement RFC 3490, see also encodings.idna. Only errors='strict' is supported.
mbcs
ansi, dbcs
Windows only: Encode the operand according to the ANSI codepage (CP_ACP).
oem
Windows only: Encode the operand according to the OEM codepage (CP_OEMCP).
New in version 3.6.
palmos
Encoding of PalmOS 3.5.
punycode
Implement RFC 3492. Stateful codecs are not supported.
raw_unicode_escape
Latin-1 encoding with \uXXXX and \UXXXXXXXX for other code points. Existing backslashes are not escaped in any way. It is used in the Python pickle protocol.
undefined
Raise an exception for all conversions, even empty strings. The error handler is ignored.
unicode_escape
Encoding suitable as the contents of a Unicode literal in ASCII-encoded Python source code, except that quotes are not escaped. Decode from Latin-1 source code. Beware that Python source code actually uses UTF-8 by default.
Changed in version 3.8: âunicode_internalâ codec is removed.
Binary Transforms¶The following codecs provide binary transforms: bytes-like object to bytes mappings. They are not supported by bytes.decode() (which only produces str output).
New in version 3.2: Restoration of the binary transforms.
Changed in version 3.4: Restoration of the aliases for the binary transforms.
Text Transforms¶The following codec provides a text transform: a str to str mapping. It is not supported by str.encode() (which only produces bytes output).
Codec
Aliases
Meaning
rot_13
rot13
Return the Caesar-cypher encryption of the operand.
New in version 3.2: Restoration of the rot_13 text transform.
Changed in version 3.4: Restoration of the rot13 alias.
encodings.idna â Internationalized Domain Names in Applications¶
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.
If you need the IDNA 2008 standard from RFC 5891 and RFC 5895, use the third-party idna module.
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 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 performs conversion between Unicode and ACE, separating an input string into labels based on the separator characters defined in section 3.1 of RFC 3490 and converting each label to ACE as required, and conversely separating an input byte string into labels based on the . separator and converting any ACE labels found into unicode. 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 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.
Return the nameprepped version of label. The implementation currently assumes query strings, so AllowUnassigned is true.
Convert a label to ASCII, as specified in RFC 3490. UseSTD3ASCIIRules is assumed to be false.
Convert a label to Unicode, as specified in RFC 3490.
encodings.mbcs â Windows ANSI codepage¶
This module implements the ANSI codepage (CP_ACP).
Availability: Windows.
Changed in version 3.2: Before 3.2, the errors argument was ignored; 'replace' was always used to encode, and 'ignore' to decode.
Changed in version 3.3: Support any error handler.
encodings.utf_8_sig â UTF-8 codec with BOM signature¶
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). On decoding, an optional UTF-8 encoded BOM at the start of the data will be skipped.
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