7.3.2.1 Built-in Codecs
Keywords: api

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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, e.g. 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, int 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. Returns `NULL` if an exception was raised by the codec.

PyObject* `PyUnicode_Encode`(const Py_UNICODE *s, int size, const char *encoding, const char *errors)
  Return value: New reference.
  Encodes the `Py_UNICODE` buffer of the given size and returns 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. Returns `NULL` if an exception was raised by the codec.

PyObject* `PyUnicode_AsEncodedString`(PyObject *unicode, const char *encoding, const char *errors)
  Return value: New reference.
  Encodes a Unicode object and returns 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. Returns `NULL` if an exception was raised by the codec.

These are the UTF-8 codec APIs:

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

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

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

These are the UTF-16 codec APIs:

PyObject* `PyUnicode_DecodeUTF16`(const char *s, int size, const char *errors, int *byteorder)
  Return value: New reference.
  Decodes length bytes from a UTF-16 encoded buffer string and returns 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.

  Returns `NULL` if an exception was raised by the codec.

PyObject* `PyUnicode_EncodeUTF16`(const Py_UNICODE *s, int size, const char *errors, int byteorder)
  Return value: New reference.
  Returns 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.

  Note that `Py_UNICODE` data is being interpreted as UTF-16 reduced to UCS-2. This trick makes it possible to add full UTF-16 capabilities at a later point without comprimising the APIs.

  Returns `NULL` if an exception was raised by the codec.

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

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

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

PyObject* `PyUnicode_EncodeUnicodeEscape`(const Py_UNICODE *s, int size, const char *errors)
  Return value: New reference.
  Encodes the `Py_UNICODE` buffer of the given size using Unicode-Escape and returns a Python string object. Returns `NULL` if an exception was raised by the codec.

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

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

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

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

PyObject* `PyUnicode_AsRawUnicodeEscapeString`(PyObject *unicode)
  Return value: New reference.
  Encodes a Unicode objects using Raw-Unicode-Escape and returns the result as Python string object. Error handling is ``strict''. Returns `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, int size, const char *errors)
  Return value: New reference.
  Creates a Unicode object by decoding size bytes of the Latin-1 encoded string s. Returns `NULL` if an exception was raised by the codec.

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

PyObject* `PyUnicode_AsLatin1String`(PyObject *unicode)
  Return value: New reference.
  Encodes a Unicode objects using Latin-1 and returns the result as Python string object. Error handling is ``strict''. Returns `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, int size, const char *errors)
  Return value: New reference.
  Creates a Unicode object by decoding size bytes of the ASCII encoded string s. Returns `NULL` if an exception was raised by the codec.

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

PyObject* `PyUnicode_AsASCIIString`(PyObject *unicode)
  Return value: New reference.
  Encodes a Unicode objects using ASCII and returns the result as Python string object. Error handling is ``strict''. Returns `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, int size, PyObject *mapping, const char *errors)
  Return value: New reference.
  Creates a Unicode object by decoding size bytes of the encoded string s using the given mapping object. Returns `NULL` if an exception was raised by the codec.

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

PyObject* `PyUnicode_AsCharmapString`(PyObject *unicode, PyObject *mapping)
  Return value: New reference.
  Encodes a Unicode objects using the given mapping object and returns the result as Python string object. Error handling is ``strict''. Returns `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, int size, PyObject *table, const char *errors)
  Return value: New reference.
  Translates a `Py_UNICODE` buffer of the given length by applying a character mapping table to it and returns the resulting Unicode object. Returns `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 method__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, int size, const char *errors)
  Return value: New reference.
  Creates a Unicode object by decoding size bytes of the MBCS encoded string s. Returns `NULL` if an exception was raised by the codec.

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

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