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7.3.2.1 Built-in Codecs


7.3.2.1 Built-in Codecs

Python provides a set of builtin codecs which are written in C for speed. All of these codecs are directly usable via the following functions.

Many of the following APIs take two arguments encoding and errors. These parameters encoding and errors have the same semantics as the ones of the builtin unicode() Unicode object constructor.

Setting encoding to NULL causes the default encoding to be used which is ASCII. The file system calls should use Py_FileSystemDefaultEncoding as the encoding for file names. This variable should be treated as read-only: On some systems, it will be a pointer to a static string, on others, it will change at run-time (such as when the application invokes setlocale).

Error handling is set by errors which may also be set to NULL meaning to use the default handling defined for the codec. Default error handling for all builtin codecs is ``strict'' (ValueError is raised).

The codecs all use a similar interface. Only deviation from the following generic ones are documented for simplicity.

These are the generic codec APIs:

PyObject* PyUnicode_Decode(const char *s, Py_ssize_t size, const char *encoding, const char *errors)
Return value: New reference.
Create a Unicode object by decoding size bytes of the encoded string s. encoding and errors have the same meaning as the parameters of the same name in the unicode() builtin function. The codec to be used is looked up using the Python codec registry. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_Encode(const Py_UNICODE *s, Py_ssize_t size, const char *encoding, const char *errors)
Return value: New reference.
Encode the Py_UNICODE buffer of the given size and return a Python string object. encoding and errors have the same meaning as the parameters of the same name in the Unicode encode() method. The codec to be used is looked up using the Python codec registry. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_AsEncodedString(PyObject *unicode, const char *encoding, const char *errors)
Return value: New reference.
Encode a Unicode object and return the result as Python string object. encoding and errors have the same meaning as the parameters of the same name in the Unicode encode() method. The codec to be used is looked up using the Python codec registry. Return NULL if an exception was raised by the codec.

These are the UTF-8 codec APIs:

PyObject* PyUnicode_DecodeUTF8(const char *s, Py_ssize_t size, const char *errors)
Return value: New reference.
Create a Unicode object by decoding size bytes of the UTF-8 encoded string s. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_DecodeUTF8Stateful(const char *s, Py_ssize_t size, const char *errors, Py_ssize_t *consumed)
Return value: New reference.
If consumed is NULL, behave like PyUnicode_DecodeUTF8(). If consumed is not NULL, trailing incomplete UTF-8 byte sequences will not be treated as an error. Those bytes will not be decoded and the number of bytes that have been decoded will be stored in consumed. New in version 2.4.

PyObject* PyUnicode_EncodeUTF8(const Py_UNICODE *s, Py_ssize_t size, const char *errors)
Return value: New reference.
Encode the Py_UNICODE buffer of the given size using UTF-8 and return a Python string object. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_AsUTF8String(PyObject *unicode)
Return value: New reference.
Encode a Unicode objects using UTF-8 and return the result as Python string object. Error handling is ``strict''. Return NULL if an exception was raised by the codec.

These are the UTF-16 codec APIs:

PyObject* PyUnicode_DecodeUTF16(const char *s, Py_ssize_t size, const char *errors, int *byteorder)
Return value: New reference.
Decode length bytes from a UTF-16 encoded buffer string and return the corresponding Unicode object. errors (if non-NULL) defines the error handling. It defaults to ``strict''.

If byteorder is non-NULL, the decoder starts decoding using the given byte order:

   *byteorder == -1: little endian
   *byteorder == 0:  native order
   *byteorder == 1:  big endian

and then switches according to all byte order marks (BOM) it finds in the input data. BOMs are not copied into the resulting Unicode string. After completion, *byteorder is set to the current byte order at the end of input data.

If byteorder is NULL, the codec starts in native order mode.

Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_DecodeUTF16Stateful(const char *s, Py_ssize_t size, const char *errors, int *byteorder, Py_ssize_t *consumed)
Return value: New reference.
If consumed is NULL, behave like PyUnicode_DecodeUTF16(). If consumed is not NULL, PyUnicode_DecodeUTF16Stateful() will not treat trailing incomplete UTF-16 byte sequences (such as an odd number of bytes or a split surrogate pair) as an error. Those bytes will not be decoded and the number of bytes that have been decoded will be stored in consumed. New in version 2.4.

PyObject* PyUnicode_EncodeUTF16(const Py_UNICODE *s, Py_ssize_t size, const char *errors, int byteorder)
Return value: New reference.
Return a Python string object holding the UTF-16 encoded value of the Unicode data in s. If byteorder is not 0, output is written according to the following byte order:

   byteorder == -1: little endian
   byteorder == 0:  native byte order (writes a BOM mark)
   byteorder == 1:  big endian

If byteorder is 0, the output string will always start with the Unicode BOM mark (U+FEFF). In the other two modes, no BOM mark is prepended.

If Py_UNICODE_WIDE is defined, a single Py_UNICODE value may get represented as a surrogate pair. If it is not defined, each Py_UNICODE values is interpreted as an UCS-2 character.

Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_AsUTF16String(PyObject *unicode)
Return value: New reference.
Return a Python string using the UTF-16 encoding in native byte order. The string always starts with a BOM mark. Error handling is ``strict''. Return NULL if an exception was raised by the codec.

These are the ``Unicode Escape'' codec APIs:

PyObject* PyUnicode_DecodeUnicodeEscape(const char *s, Py_ssize_t size, const char *errors)
Return value: New reference.
Create a Unicode object by decoding size bytes of the Unicode-Escape encoded string s. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_EncodeUnicodeEscape(const Py_UNICODE *s, Py_ssize_t size)
Return value: New reference.
Encode the Py_UNICODE buffer of the given size using Unicode-Escape and return a Python string object. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_AsUnicodeEscapeString(PyObject *unicode)
Return value: New reference.
Encode a Unicode objects using Unicode-Escape and return the result as Python string object. Error handling is ``strict''. Return NULL if an exception was raised by the codec.

These are the ``Raw Unicode Escape'' codec APIs:

PyObject* PyUnicode_DecodeRawUnicodeEscape(const char *s, Py_ssize_t size, const char *errors)
Return value: New reference.
Create a Unicode object by decoding size bytes of the Raw-Unicode-Escape encoded string s. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_EncodeRawUnicodeEscape(const Py_UNICODE *s, Py_ssize_t size, const char *errors)
Return value: New reference.
Encode the Py_UNICODE buffer of the given size using Raw-Unicode-Escape and return a Python string object. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_AsRawUnicodeEscapeString(PyObject *unicode)
Return value: New reference.
Encode a Unicode objects using Raw-Unicode-Escape and return the result as Python string object. Error handling is ``strict''. Return NULL if an exception was raised by the codec.

These are the Latin-1 codec APIs: Latin-1 corresponds to the first 256 Unicode ordinals and only these are accepted by the codecs during encoding.

PyObject* PyUnicode_DecodeLatin1(const char *s, Py_ssize_t size, const char *errors)
Return value: New reference.
Create a Unicode object by decoding size bytes of the Latin-1 encoded string s. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_EncodeLatin1(const Py_UNICODE *s, Py_ssize_t size, const char *errors)
Return value: New reference.
Encode the Py_UNICODE buffer of the given size using Latin-1 and return a Python string object. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_AsLatin1String(PyObject *unicode)
Return value: New reference.
Encode a Unicode objects using Latin-1 and return the result as Python string object. Error handling is ``strict''. Return NULL if an exception was raised by the codec.

These are the ASCII codec APIs. Only 7-bit ASCII data is accepted. All other codes generate errors.

PyObject* PyUnicode_DecodeASCII(const char *s, Py_ssize_t size, const char *errors)
Return value: New reference.
Create a Unicode object by decoding size bytes of the ASCII encoded string s. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_EncodeASCII(const Py_UNICODE *s, Py_ssize_t size, const char *errors)
Return value: New reference.
Encode the Py_UNICODE buffer of the given size using ASCII and return a Python string object. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_AsASCIIString(PyObject *unicode)
Return value: New reference.
Encode a Unicode objects using ASCII and return the result as Python string object. Error handling is ``strict''. Return NULL if an exception was raised by the codec.

These are the mapping codec APIs:

This codec is special in that it can be used to implement many different codecs (and this is in fact what was done to obtain most of the standard codecs included in the encodings package). The codec uses mapping to encode and decode characters.

Decoding mappings must map single string characters to single Unicode characters, integers (which are then interpreted as Unicode ordinals) or None (meaning "undefined mapping" and causing an error).

Encoding mappings must map single Unicode characters to single string characters, integers (which are then interpreted as Latin-1 ordinals) or None (meaning "undefined mapping" and causing an error).

The mapping objects provided must only support the __getitem__ mapping interface.

If a character lookup fails with a LookupError, the character is copied as-is meaning that its ordinal value will be interpreted as Unicode or Latin-1 ordinal resp. Because of this, mappings only need to contain those mappings which map characters to different code points.

PyObject* PyUnicode_DecodeCharmap(const char *s, Py_ssize_t size, PyObject *mapping, const char *errors)
Return value: New reference.
Create a Unicode object by decoding size bytes of the encoded string s using the given mapping object. Return NULL if an exception was raised by the codec. If mapping is NULL latin-1 decoding will be done. Else it can be a dictionary mapping byte or a unicode string, which is treated as a lookup table. Byte values greater that the length of the string and U+FFFE "characters" are treated as "undefined mapping". Changed in version 2.4: Allowed unicode string as mapping argument.

PyObject* PyUnicode_EncodeCharmap(const Py_UNICODE *s, Py_ssize_t size, PyObject *mapping, const char *errors)
Return value: New reference.
Encode the Py_UNICODE buffer of the given size using the given mapping object and return a Python string object. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_AsCharmapString(PyObject *unicode, PyObject *mapping)
Return value: New reference.
Encode a Unicode objects using the given mapping object and return the result as Python string object. Error handling is ``strict''. Return NULL if an exception was raised by the codec.

The following codec API is special in that maps Unicode to Unicode.

PyObject* PyUnicode_TranslateCharmap(const Py_UNICODE *s, Py_ssize_t size, PyObject *table, const char *errors)
Return value: New reference.
Translate a Py_UNICODE buffer of the given length by applying a character mapping table to it and return the resulting Unicode object. Return NULL when an exception was raised by the codec.

The mapping table must map Unicode ordinal integers to Unicode ordinal integers or None (causing deletion of the character).

Mapping tables need only provide the __getitem__() interface; dictionaries and sequences work well. Unmapped character ordinals (ones which cause a LookupError) are left untouched and are copied as-is.

These are the MBCS codec APIs. They are currently only available on Windows and use the Win32 MBCS converters to implement the conversions. Note that MBCS (or DBCS) is a class of encodings, not just one. The target encoding is defined by the user settings on the machine running the codec.

PyObject* PyUnicode_DecodeMBCS(const char *s, Py_ssize_t size, const char *errors)
Return value: New reference.
Create a Unicode object by decoding size bytes of the MBCS encoded string s. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_DecodeMBCSStateful(const char *s, int size, const char *errors, int *consumed)
If consumed is NULL, behave like PyUnicode_DecodeMBCS(). If consumed is not NULL, PyUnicode_DecodeMBCSStateful() will not decode trailing lead byte and the number of bytes that have been decoded will be stored in consumed. New in version 2.5.

PyObject* PyUnicode_EncodeMBCS(const Py_UNICODE *s, Py_ssize_t size, const char *errors)
Return value: New reference.
Encode the Py_UNICODE buffer of the given size using MBCS and return a Python string object. Return NULL if an exception was raised by the codec.

PyObject* PyUnicode_AsMBCSString(PyObject *unicode)
Return value: New reference.
Encode a Unicode objects using MBCS and return the result as Python string object. Error handling is ``strict''. Return NULL if an exception was raised by the codec.

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