.. highlightlang:: c

.. _unicodeobjects:

Unicode Objects and Codecs

--------------------------

.. sectionauthor:: Marc-Andre Lemburg <mal@lemburg.com>

Unicode Objects

^^^^^^^^^^^^^^^

These are the basic Unicode object types used for the Unicode implementation in

Python:

.. % --- Unicode Type -------------------------------------------------------

.. ctype:: Py_UNICODE

   This type represents the storage type which is used by Python internally as

   basis for holding Unicode ordinals.  Python's default builds use a 16-bit type

   for :ctype:`Py_UNICODE` and store Unicode values internally as UCS2. It is also

   possible to build a UCS4 version of Python (most recent Linux distributions come

   with UCS4 builds of Python). These builds then use a 32-bit type for

   :ctype:`Py_UNICODE` and store Unicode data internally as UCS4. On platforms

   where :ctype:`wchar_t` is available and compatible with the chosen Python

   Unicode build variant, :ctype:`Py_UNICODE` is a typedef alias for

   :ctype:`wchar_t` to enhance native platform compatibility. On all other

   platforms, :ctype:`Py_UNICODE` is a typedef alias for either :ctype:`unsigned

   short` (UCS2) or :ctype:`unsigned long` (UCS4).

Note that UCS2 and UCS4 Python builds are not binary compatible. Please keep

this in mind when writing extensions or interfaces.

.. ctype:: PyUnicodeObject

   This subtype of :ctype:`PyObject` represents a Python Unicode object.

.. cvar:: PyTypeObject PyUnicode_Type

   This instance of :ctype:`PyTypeObject` represents the Python Unicode type.  It

   is exposed to Python code as ``unicode`` and ``types.UnicodeType``.

The following APIs are really C macros and can be used to do fast checks and to

access internal read-only data of Unicode objects:

.. cfunction:: int PyUnicode_Check(PyObject *o)

   Return true if the object *o* is a Unicode object or an instance of a Unicode

   subtype.

   .. versionchanged:: 2.2

      Allowed subtypes to be accepted.

.. cfunction:: int PyUnicode_CheckExact(PyObject *o)

   Return true if the object *o* is a Unicode object, but not an instance of a

   subtype.

   .. versionadded:: 2.2

.. cfunction:: Py_ssize_t PyUnicode_GET_SIZE(PyObject *o)

   Return the size of the object.  *o* has to be a :ctype:`PyUnicodeObject` (not

   checked).

.. cfunction:: Py_ssize_t PyUnicode_GET_DATA_SIZE(PyObject *o)

   Return the size of the object's internal buffer in bytes.  *o* has to be a

   :ctype:`PyUnicodeObject` (not checked).

.. cfunction:: Py_UNICODE* PyUnicode_AS_UNICODE(PyObject *o)

   Return a pointer to the internal :ctype:`Py_UNICODE` buffer of the object.  *o*

   has to be a :ctype:`PyUnicodeObject` (not checked).

.. cfunction:: const char* PyUnicode_AS_DATA(PyObject *o)

   Return a pointer to the internal buffer of the object. *o* has to be a

   :ctype:`PyUnicodeObject` (not checked).

.. cfunction:: int PyUnicode_ClearFreeList(void)

   Clear the free list. Return the total number of freed items.

   .. versionadded:: 2.6

Unicode provides many different character properties. The most often needed ones

are available through these macros which are mapped to C functions depending on

the Python configuration.

.. % --- Unicode character properties ---------------------------------------

.. cfunction:: int Py_UNICODE_ISSPACE(Py_UNICODE ch)

   Return 1 or 0 depending on whether *ch* is a whitespace character.

.. cfunction:: int Py_UNICODE_ISLOWER(Py_UNICODE ch)

   Return 1 or 0 depending on whether *ch* is a lowercase character.

.. cfunction:: int Py_UNICODE_ISUPPER(Py_UNICODE ch)

   Return 1 or 0 depending on whether *ch* is an uppercase character.

.. cfunction:: int Py_UNICODE_ISTITLE(Py_UNICODE ch)

   Return 1 or 0 depending on whether *ch* is a titlecase character.

.. cfunction:: int Py_UNICODE_ISLINEBREAK(Py_UNICODE ch)

   Return 1 or 0 depending on whether *ch* is a linebreak character.

.. cfunction:: int Py_UNICODE_ISDECIMAL(Py_UNICODE ch)

   Return 1 or 0 depending on whether *ch* is a decimal character.

.. cfunction:: int Py_UNICODE_ISDIGIT(Py_UNICODE ch)

   Return 1 or 0 depending on whether *ch* is a digit character.

.. cfunction:: int Py_UNICODE_ISNUMERIC(Py_UNICODE ch)

   Return 1 or 0 depending on whether *ch* is a numeric character.

.. cfunction:: int Py_UNICODE_ISALPHA(Py_UNICODE ch)

   Return 1 or 0 depending on whether *ch* is an alphabetic character.

.. cfunction:: int Py_UNICODE_ISALNUM(Py_UNICODE ch)

   Return 1 or 0 depending on whether *ch* is an alphanumeric character.

These APIs can be used for fast direct character conversions:

.. cfunction:: Py_UNICODE Py_UNICODE_TOLOWER(Py_UNICODE ch)

   Return the character *ch* converted to lower case.

.. cfunction:: Py_UNICODE Py_UNICODE_TOUPPER(Py_UNICODE ch)

   Return the character *ch* converted to upper case.

.. cfunction:: Py_UNICODE Py_UNICODE_TOTITLE(Py_UNICODE ch)

   Return the character *ch* converted to title case.

.. cfunction:: int Py_UNICODE_TODECIMAL(Py_UNICODE ch)

   Return the character *ch* converted to a decimal positive integer.  Return

   ``-1`` if this is not possible.  This macro does not raise exceptions.

.. cfunction:: int Py_UNICODE_TODIGIT(Py_UNICODE ch)

   Return the character *ch* converted to a single digit integer. Return ``-1`` if

   this is not possible.  This macro does not raise exceptions.

.. cfunction:: double Py_UNICODE_TONUMERIC(Py_UNICODE ch)

   Return the character *ch* converted to a double. Return ``-1.0`` if this is not

   possible.  This macro does not raise exceptions.

To create Unicode objects and access their basic sequence properties, use these

APIs:

.. % --- Plain Py_UNICODE ---------------------------------------------------

.. cfunction:: PyObject* PyUnicode_FromUnicode(const Py_UNICODE *u, Py_ssize_t size)

   Create a Unicode Object from the Py_UNICODE buffer *u* of the given size. *u*

   may be *NULL* which causes the contents to be undefined. It is the user's

   responsibility to fill in the needed data.  The buffer is copied into the new

   object. If the buffer is not *NULL*, the return value might be a shared object.

   Therefore, modification of the resulting Unicode object is only allowed when *u*

   is *NULL*.

.. cfunction:: Py_UNICODE* PyUnicode_AsUnicode(PyObject *unicode)

   Return a read-only pointer to the Unicode object's internal :ctype:`Py_UNICODE`

   buffer, *NULL* if *unicode* is not a Unicode object.

.. cfunction:: Py_ssize_t PyUnicode_GetSize(PyObject *unicode)

   Return the length of the Unicode object.

.. cfunction:: PyObject* PyUnicode_FromEncodedObject(PyObject *obj, const char *encoding, const char *errors)

   Coerce an encoded object *obj* to an Unicode object and return a reference with

   incremented refcount.

   String and other char buffer compatible objects are decoded according to the

   given encoding and using the error handling defined by errors.  Both can be

   *NULL* to have the interface use the default values (see the next section for

   details).

   All other objects, including Unicode objects, cause a :exc:`TypeError` to be

   set.

   The API returns *NULL* if there was an error.  The caller is responsible for

   decref'ing the returned objects.

.. cfunction:: PyObject* PyUnicode_FromObject(PyObject *obj)

   Shortcut for ``PyUnicode_FromEncodedObject(obj, NULL, "strict")`` which is used

   throughout the interpreter whenever coercion to Unicode is needed.

If the platform supports :ctype:`wchar_t` and provides a header file wchar.h,

Python can interface directly to this type using the following functions.

Support is optimized if Python's own :ctype:`Py_UNICODE` type is identical to

the system's :ctype:`wchar_t`.

.. % --- wchar_t support for platforms which support it ---------------------

.. cfunction:: PyObject* PyUnicode_FromWideChar(const wchar_t *w, Py_ssize_t size)

   Create a Unicode object from the :ctype:`wchar_t` buffer *w* of the given size.

   Return *NULL* on failure.

.. cfunction:: Py_ssize_t PyUnicode_AsWideChar(PyUnicodeObject *unicode, wchar_t *w, Py_ssize_t size)

   Copy the Unicode object contents into the :ctype:`wchar_t` buffer *w*.  At most

   *size* :ctype:`wchar_t` characters are copied (excluding a possibly trailing

   0-termination character).  Return the number of :ctype:`wchar_t` characters

   copied or -1 in case of an error.  Note that the resulting :ctype:`wchar_t`

   string may or may not be 0-terminated.  It is the responsibility of the caller

   to make sure that the :ctype:`wchar_t` string is 0-terminated in case this is

   required by the application.

.. _builtincodecs:

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 :cdata:`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" (:exc:`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:

.. % --- Generic Codecs -----------------------------------------------------

.. cfunction:: PyObject* PyUnicode_Decode(const char *s, Py_ssize_t size, const char *encoding, const char *errors)

   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 :func:`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.

.. cfunction:: PyObject* PyUnicode_Encode(const Py_UNICODE *s, Py_ssize_t size, const char *encoding, const char *errors)

   Encode the :ctype:`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 :meth:`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.

.. cfunction:: PyObject* PyUnicode_AsEncodedString(PyObject *unicode, const char *encoding, const char *errors)

   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 :meth:`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:

.. % --- UTF-8 Codecs -------------------------------------------------------

.. cfunction:: PyObject* PyUnicode_DecodeUTF8(const char *s, Py_ssize_t size, const char *errors)

   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.

.. cfunction:: PyObject* PyUnicode_DecodeUTF8Stateful(const char *s, Py_ssize_t size, const char *errors, Py_ssize_t *consumed)

   If *consumed* is *NULL*, behave like :cfunc:`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*.

   .. versionadded:: 2.4

.. cfunction:: PyObject* PyUnicode_EncodeUTF8(const Py_UNICODE *s, Py_ssize_t size, const char *errors)

   Encode the :ctype:`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.

.. cfunction:: PyObject* PyUnicode_AsUTF8String(PyObject *unicode)

   Encode a Unicode object 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-32 codec APIs:

.. % --- UTF-32 Codecs ------------------------------------------------------ */

.. cfunction:: PyObject* PyUnicode_DecodeUTF32(const char *s, Py_ssize_t size, const char *errors, int *byteorder)

   Decode *length* bytes from a UTF-32 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 if the first four bytes of the input data are a byte order mark

   (BOM) and the specified byte order is native order.  This BOM is not copied into

   the resulting Unicode string.  After completion, *\*byteorder* is set to the

   current byte order at the end of input data.

   In a narrow build codepoints outside the BMP will be decoded as surrogate pairs.

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

   Return *NULL* if an exception was raised by the codec.

   .. versionadded:: 2.6

.. cfunction:: PyObject* PyUnicode_DecodeUTF32Stateful(const char *s, Py_ssize_t size, const char *errors, int *byteorder, Py_ssize_t *consumed)

   If *consumed* is *NULL*, behave like :cfunc:`PyUnicode_DecodeUTF32`. If

   *consumed* is not *NULL*, :cfunc:`PyUnicode_DecodeUTF32Stateful` will not treat

   trailing incomplete UTF-32 byte sequences (such as a number of bytes not divisible

   by four) as an error. Those bytes will not be decoded and the number of bytes

   that have been decoded will be stored in *consumed*.

   .. versionadded:: 2.6

.. cfunction:: PyObject* PyUnicode_EncodeUTF32(const Py_UNICODE *s, Py_ssize_t size, const char *errors, int byteorder)

   Return a Python bytes object holding the UTF-32 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 not defined, surrogate pairs will be output

   as a single codepoint.

   Return *NULL* if an exception was raised by the codec.

   .. versionadded:: 2.6

.. cfunction:: PyObject* PyUnicode_AsUTF32String(PyObject *unicode)

   Return a Python string using the UTF-32 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.

   .. versionadded:: 2.6

These are the UTF-16 codec APIs:

.. % --- UTF-16 Codecs ------------------------------------------------------ */

.. cfunction:: PyObject* PyUnicode_DecodeUTF16(const char *s, Py_ssize_t size, const char *errors, int *byteorder)

   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 if the first two bytes of the input data are a byte order mark

   (BOM) and the specified byte order is native order.  This BOM is not copied into

   the resulting Unicode string.  After completion, *\*byteorder* is set to the

   current byte order at the.

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

   Return *NULL* if an exception was raised by the codec.

.. cfunction:: PyObject* PyUnicode_DecodeUTF16Stateful(const char *s, Py_ssize_t size, const char *errors, int *byteorder, Py_ssize_t *consumed)

   If *consumed* is *NULL*, behave like :cfunc:`PyUnicode_DecodeUTF16`. If

   *consumed* is not *NULL*, :cfunc:`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*.

   .. versionadded:: 2.4

.. cfunction:: PyObject* PyUnicode_EncodeUTF16(const Py_UNICODE *s, Py_ssize_t size, const char *errors, int byteorder)

   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 :ctype:`Py_UNICODE` value may get

   represented as a surrogate pair. If it is not defined, each :ctype:`Py_UNICODE`

   values is interpreted as an UCS-2 character.

   Return *NULL* if an exception was raised by the codec.

.. cfunction:: PyObject* PyUnicode_AsUTF16String(PyObject *unicode)

   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:

.. % --- Unicode-Escape Codecs ----------------------------------------------

.. cfunction:: PyObject* PyUnicode_DecodeUnicodeEscape(const char *s, Py_ssize_t size, const char *errors)

   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.

.. cfunction:: PyObject* PyUnicode_EncodeUnicodeEscape(const Py_UNICODE *s, Py_ssize_t size)

   Encode the :ctype:`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.

.. cfunction:: PyObject* PyUnicode_AsUnicodeEscapeString(PyObject *unicode)

   Encode a Unicode object 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:

.. % --- Raw-Unicode-Escape Codecs ------------------------------------------

.. cfunction:: PyObject* PyUnicode_DecodeRawUnicodeEscape(const char *s, Py_ssize_t size, const char *errors)

   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.

.. cfunction:: PyObject* PyUnicode_EncodeRawUnicodeEscape(const Py_UNICODE *s, Py_ssize_t size, const char *errors)

   Encode the :ctype:`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