Unicode Objects and Codecs

Unicode Objects

Since the implementation of PEP 393 in Python 3.3, Unicode objects internally use a variety of representations, in order to allow handling the complete range of Unicode characters while staying memory efficient. There are special cases for strings where all code points are below 128, 256, or 65536; otherwise, code points must be below 1114112 (which is the full Unicode range).

UTF-8 representation is created on demand and cached in the Unicode object.

Note

The Py_UNICODE representation has been removed since Python 3.12 with deprecated APIs. See PEP 623 for more information.

Unicode Type

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

type Py_UCS4

type Py_UCS2

type Py_UCS1

Part of the Stable ABI.

These types are typedefs for unsigned integer types wide enough to contain characters of 32 bits, 16 bits and 8 bits, respectively. When dealing with single Unicode characters, use Py_UCS4.

Added in version 3.3.

type Py_UNICODE

This is a typedef of wchar_t, which is a 16-bit type or 32-bit type depending on the platform.

Changed in version 3.3: In previous versions, this was a 16-bit type or a 32-bit type depending on whether you selected a “narrow” or “wide” Unicode version of Python at build time.

Deprecated since version 3.13, will be removed in version 3.15.

type PyASCIIObject

type PyCompactUnicodeObject

type PyUnicodeObject

These subtypes of PyObject represent a Python Unicode object. In almost all cases, they shouldn’t be used directly, since all API functions that deal with Unicode objects take and return PyObject pointers.

Added in version 3.3.

PyTypeObject PyUnicode_Type

Part of the Stable ABI.

This instance of PyTypeObject represents the Python Unicode type. It is exposed to Python code as str.

The following APIs are C macros and static inlined functions for fast checks and access to internal read-only data of Unicode objects:

int PyUnicode_Check(PyObject *obj)

Return true if the object obj is a Unicode object or an instance of a Unicode subtype. This function always succeeds.

int PyUnicode_CheckExact(PyObject *obj)

Return true if the object obj is a Unicode object, but not an instance of a subtype. This function always succeeds.

int PyUnicode_READY(PyObject *unicode)

Returns 0. This API is kept only for backward compatibility.

Added in version 3.3.

Deprecated since version 3.10: This API does nothing since Python 3.12.

Py_ssize_t PyUnicode_GET_LENGTH(PyObject *unicode)

Return the length of the Unicode string, in code points. unicode has to be a Unicode object in the “canonical” representation (not checked).

Added in version 3.3.

Py_UCS1 *PyUnicode_1BYTE_DATA(PyObject *unicode)

Py_UCS2 *PyUnicode_2BYTE_DATA(PyObject *unicode)

Py_UCS4 *PyUnicode_4BYTE_DATA(PyObject *unicode)

Return a pointer to the canonical representation cast to UCS1, UCS2 or UCS4 integer types for direct character access. No checks are performed if the canonical representation has the correct character size; use PyUnicode_KIND() to select the right function.

Added in version 3.3.

PyUnicode_1BYTE_KIND

PyUnicode_2BYTE_KIND

PyUnicode_4BYTE_KIND

Return values of the PyUnicode_KIND() macro.

Added in version 3.3.

Changed in version 3.12: PyUnicode_WCHAR_KIND has been removed.

int PyUnicode_KIND(PyObject *unicode)

Return one of the PyUnicode kind constants (see above) that indicate how many bytes per character this Unicode object uses to store its data. unicode has to be a Unicode object in the “canonical” representation (not checked).

Added in version 3.3.

void *PyUnicode_DATA(PyObject *unicode)

Return a void pointer to the raw Unicode buffer. unicode has to be a Unicode object in the “canonical” representation (not checked).

Added in version 3.3.

void PyUnicode_WRITE(int kind, void *data, Py_ssize_t index, Py_UCS4 value)

Write into a canonical representation data (as obtained with PyUnicode_DATA()). This function performs no sanity checks, and is intended for usage in loops. The caller should cache the kind value and data pointer as obtained from other calls. index is the index in the string (starts at 0) and value is the new code point value which should be written to that location.

Added in version 3.3.

Py_UCS4 PyUnicode_READ(int kind, void *data, Py_ssize_t index)

Read a code point from a canonical representation data (as obtained with PyUnicode_DATA()). No checks or ready calls are performed.

Added in version 3.3.

Py_UCS4 PyUnicode_READ_CHAR(PyObject *unicode, Py_ssize_t index)

Read a character from a Unicode object unicode, which must be in the “canonical” representation. This is less efficient than PyUnicode_READ() if you do multiple consecutive reads.

Added in version 3.3.

Py_UCS4 PyUnicode_MAX_CHAR_VALUE(PyObject *unicode)

Return the maximum code point that is suitable for creating another string based on unicode, which must be in the “canonical” representation. This is always an approximation but more efficient than iterating over the string.

Added in version 3.3.

int PyUnicode_IsIdentifier(PyObject *unicode)

Part of the Stable ABI.

Return 1 if the string is a valid identifier according to the language definition, section Identifiers and keywords. Return 0 otherwise.

Changed in version 3.9: The function does not call Py_FatalError() anymore if the string is not ready.

Unicode Character Properties

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.

int Py_UNICODE_ISSPACE(Py_UCS4 ch)

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

int Py_UNICODE_ISLOWER(Py_UCS4 ch)

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

int Py_UNICODE_ISUPPER(Py_UCS4 ch)

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

int Py_UNICODE_ISTITLE(Py_UCS4 ch)

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

int Py_UNICODE_ISLINEBREAK(Py_UCS4 ch)

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

int Py_UNICODE_ISDECIMAL(Py_UCS4 ch)

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

int Py_UNICODE_ISDIGIT(Py_UCS4 ch)

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

int Py_UNICODE_ISNUMERIC(Py_UCS4 ch)

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

int Py_UNICODE_ISALPHA(Py_UCS4 ch)

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

int Py_UNICODE_ISALNUM(Py_UCS4 ch)

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

int Py_UNICODE_ISPRINTABLE(Py_UCS4 ch)

Return 1 or 0 depending on whether ch is a printable character. Nonprintable characters are those characters defined in the Unicode character database as “Other” or “Separator”, excepting the ASCII space (0x20) which is considered printable. (Note that printable characters in this context are those which should not be escaped when repr() is invoked on a string. It has no bearing on the handling of strings written to sys.stdout or sys.stderr.)

These APIs can be used for fast direct character conversions:

Py_UCS4 Py_UNICODE_TOLOWER(Py_UCS4 ch)

Return the character ch converted to lower case.

Py_UCS4 Py_UNICODE_TOUPPER(Py_UCS4 ch)

Return the character ch converted to upper case.

Py_UCS4 Py_UNICODE_TOTITLE(Py_UCS4 ch)

Return the character ch converted to title case.

int Py_UNICODE_TODECIMAL(Py_UCS4 ch)

Return the character ch converted to a decimal positive integer. Return -1 if this is not possible. This function does not raise exceptions.

int Py_UNICODE_TODIGIT(Py_UCS4 ch)

Return the character ch converted to a single digit integer. Return -1 if this is not possible. This function does not raise exceptions.

double Py_UNICODE_TONUMERIC(Py_UCS4 ch)

Return the character ch converted to a double. Return -1.0 if this is not possible. This function does not raise exceptions.

These APIs can be used to work with surrogates:

int Py_UNICODE_IS_SURROGATE(Py_UCS4 ch)

Check if ch is a surrogate (0xD800 <= ch <= 0xDFFF).

int Py_UNICODE_IS_HIGH_SURROGATE(Py_UCS4 ch)

Check if ch is a high surrogate (0xD800 <= ch <= 0xDBFF).

int Py_UNICODE_IS_LOW_SURROGATE(Py_UCS4 ch)

Check if ch is a low surrogate (0xDC00 <= ch <= 0xDFFF).

Py_UCS4 Py_UNICODE_JOIN_SURROGATES(Py_UCS4 high, Py_UCS4 low)

Join two surrogate code points and return a single Py_UCS4 value. high and low are respectively the leading and trailing surrogates in a surrogate pair. high must be in the range [0xD800; 0xDBFF] and low must be in the range [0xDC00; 0xDFFF].

Creating and accessing Unicode strings

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

PyObject *PyUnicode_New(Py_ssize_t size, Py_UCS4 maxchar)

Return value: New reference.

Create a new Unicode object. maxchar should be the true maximum code point to be placed in the string. As an approximation, it can be rounded up to the nearest value in the sequence 127, 255, 65535, 1114111.

This is the recommended way to allocate a new Unicode object. Objects created using this function are not resizable.

On error, set an exception and return NULL.

Added in version 3.3.

PyObject *PyUnicode_FromKindAndData(int kind, const void *buffer, Py_ssize_t size)

Return value: New reference.

Create a new Unicode object with the given kind (possible values are PyUnicode_1BYTE_KIND etc., as returned by PyUnicode_KIND()). The buffer must point to an array of size units of 1, 2 or 4 bytes per character, as given by the kind.

If necessary, the input buffer is copied and transformed into the canonical representation. For example, if the buffer is a UCS4 string (PyUnicode_4BYTE_KIND) and it consists only of codepoints in the UCS1 range, it will be transformed into UCS1 (PyUnicode_1BYTE_KIND).

Added in version 3.3.

PyObject *PyUnicode_FromStringAndSize(const char *str, Py_ssize_t size)

Return value: New reference. Part of the Stable ABI.

Create a Unicode object from the char buffer str. The bytes will be interpreted as being UTF-8 encoded. The buffer is copied into the new object. The return value might be a shared object, i.e. modification of the data is not allowed.

This function raises SystemError when:

• size < 0,

• str is NULL and size > 0

Changed in version 3.12: str == NULL with size > 0 is not allowed anymore.

PyObject *PyUnicode_FromString(const char *str)

Return value: New reference. Part of the Stable ABI.

Create a Unicode object from a UTF-8 encoded null-terminated char buffer str.

PyObject *PyUnicode_FromFormat(const char *format, ...)

Return value: New reference. Part of the Stable ABI.

Take a C printf()-style format string and a variable number of arguments, calculate the size of the resulting Python Unicode string and return a string with the values formatted into it. The variable arguments must be C types and must correspond exactly to the format characters in the format ASCII-encoded string.

A conversion specifier contains two or more characters and has the following components, which must occur in this order:

1. The '%' character, which marks the start of the specifier.

2. Conversion flags (optional), which affect the result of some conversion types.

3. Minimum field width (optional). If specified as an '*' (asterisk), the actual width is given in the next argument, which must be of type int, and the object to convert comes after the minimum field width and optional precision.

4. Precision (optional), given as a '.' (dot) followed by the precision. If specified as '*' (an asterisk), the actual precision is given in the next argument, which must be of type int, and the value to convert comes after the precision.

5. Length modifier (optional).

6. Conversion type.

The conversion flag characters are:

Flag	Meaning
0	The conversion will be zero padded for numeric values.
-	The converted value is left adjusted (overrides the 0 flag if both are given).

The length modifiers for following integer conversions (d, i, o, u, x, or X) specify the type of the argument (int by default):

Modifier	Types
l	long or unsigned long
ll	long long or unsigned long long
j	intmax_t or uintmax_t
z	size_t or ssize_t
t	ptrdiff_t

The length modifier l for following conversions s or V specify that the type of the argument is const wchar_t*.

The conversion specifiers are:

Conversion Specifier	Type	Comment
%	n/a	The literal % character.
d, i	Specified by the length modifier	The decimal representation of a signed C integer.
u	Specified by the length modifier	The decimal representation of an unsigned C integer.
o	Specified by the length modifier	The octal representation of an unsigned C integer.
x	Specified by the length modifier	The hexadecimal representation of an unsigned C integer (lowercase).
X	Specified by the length modifier	The hexadecimal representation of an unsigned C integer (uppercase).
c	int	A single character.
s	const char* or const wchar_t*	A null-terminated C character array.
p	const void*	The hex representation of a C pointer. Mostly equivalent to printf("%p") except that it is guaranteed to start with the literal 0x regardless of what the platform’s printf yields.
A	PyObject*	The result of calling ascii().
U	PyObject*	A Unicode object.
V	PyObject*, const char* or const wchar_t*	A Unicode object (which may be NULL) and a null-terminated C character array as a second parameter (which will be used, if the first parameter is NULL).
S	PyObject*	The result of calling PyObject_Str().
R	PyObject*	The result of calling PyObject_Repr().
T	PyObject*	Get the fully qualified name of an object type; call PyType_GetFullyQualifiedName().
#T	PyObject*	Similar to T format, but use a colon (:) as separator between the module name and the qualified name.
N	PyTypeObject*	Get the fully qualified name of a type; call PyType_GetFullyQualifiedName().
#N	PyTypeObject*	Similar to N format, but use a colon (:) as separator between the module name and the qualified name.

Note

The width formatter unit is number of characters rather than bytes. The precision formatter unit is number of bytes or wchar_t items (if the length modifier l is used) for "%s" and "%V" (if the PyObject* argument is NULL), and a number of characters for "%A", "%U", "%S", "%R" and "%V" (if the PyObject* argument is not NULL).

Note

Unlike to C printf() the 0 flag has effect even when a precision is given for integer conversions (d, i, u, o, x, or X).

Changed in version 3.2: Support for "%lld" and "%llu" added.

Changed in version 3.3: Support for "%li", "%lli" and "%zi" added.

Changed in version 3.4: Support width and precision formatter for "%s", "%A", "%U", "%V", "%S", "%R" added.

Changed in version 3.12: Support for conversion specifiers o and X. Support for length modifiers j and t. Length modifiers are now applied to all integer conversions. Length modifier l is now applied to conversion specifiers s and V. Support for variable width and precision *. Support for flag -.

An unrecognized format character now sets a SystemError. In previous versions it caused all the rest of the format string to be copied as-is to the result string, and any extra arguments discarded.

Changed in version 3.13: Support for %T, %#T, %N and %#N formats added.

PyObject *PyUnicode_FromFormatV(const char *format, va_list vargs)

Return value: New reference. Part of the Stable ABI.

Identical to PyUnicode_FromFormat() except that it takes exactly two arguments.

PyObject *PyUnicode_FromObject(PyObject *obj)

Return value: New reference. Part of the Stable ABI.

Copy an instance of a Unicode subtype to a new true Unicode object if necessary. If obj is already a true Unicode object (not a subtype), return a new strong reference to the object.

Objects other than Unicode or its subtypes will cause a TypeError.

PyObject *PyUnicode_FromEncodedObject(PyObject *obj, const char *encoding, const char *errors)

Return value: New reference. Part of the Stable ABI.

Decode an encoded object obj to a Unicode object.

bytes, bytearray and other bytes-like 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 Built-in Codecs for details).

All other objects, including Unicode objects, cause a TypeError to be set.

The API returns NULL if there was an error. The caller is responsible for decref’ing the returned objects.

Py_ssize_t PyUnicode_GetLength(PyObject *unicode)

Part of the Stable ABI since version 3.7.

Return the length of the Unicode object, in code points.

On error, set an exception and return -1.

Added in version 3.3.

Py_ssize_t PyUnicode_CopyCharacters(PyObject *to, Py_ssize_t to_start, PyObject *from, Py_ssize_t from_start, Py_ssize_t how_many)

Copy characters from one Unicode object into another. This function performs character conversion when necessary and falls back to memcpy() if possible. Returns -1 and sets an exception on error, otherwise returns the number of copied characters.

Added in version 3.3.

Py_ssize_t PyUnicode_Fill(PyObject *unicode, Py_ssize_t start, Py_ssize_t length, Py_UCS4 fill_char)

Fill a string with a character: write fill_char into unicode[start:start+length].

Fail if fill_char is bigger than the string maximum character, or if the string has more than 1 reference.

Return the number of written character, or return -1 and raise an exception on error.

Added in version 3.3.

int PyUnicode_WriteChar(PyObject *unicode, Py_ssize_t index, Py_UCS4 character)

Part of the Stable ABI since version 3.7.

Write a character to a string. The string must have been created through PyUnicode_New(). Since Unicode strings are supposed to be immutable, the string must not be shared, or have been hashed yet.

This function checks that unicode is a Unicode object, that the index is not out of bounds, and that the object can be modified safely (i.e. that it its reference count is one).

Return 0 on success, -1 on error with an exception set.

Added in version 3.3.

Py_UCS4 PyUnicode_ReadChar(PyObject *unicode, Py_ssize_t index)

Part of the Stable ABI since version 3.7.

Read a character from a string. This function checks that unicode is a Unicode object and the index is not out of bounds, in contrast to PyUnicode_READ_CHAR(), which performs no error checking.

Return character on success, -1 on error with an exception set.

Added in version 3.3.

PyObject *PyUnicode_Substring(PyObject *unicode, Py_ssize_t start, Py_ssize_t end)

Return value: New reference. Part of the Stable ABI since version 3.7.

Return a substring of unicode, from character index start (included) to character index end (excluded). Negative indices are not supported. On error, set an exception and return NULL.

Added in version 3.3.

Py_UCS4 *PyUnicode_AsUCS4(PyObject *unicode, Py_UCS4 *buffer, Py_ssize_t buflen, int copy_null)

Part of the Stable ABI since version 3.7.

Copy the string unicode into a UCS4 buffer, including a null character, if copy_null is set. Returns NULL and sets an exception on error (in particular, a SystemError if buflen is smaller than the length of unicode). buffer is returned on success.

Added in version 3.3.

Py_UCS4 *PyUnicode_AsUCS4Copy(PyObject *unicode)

Part of the Stable ABI since version 3.7.

Copy the string unicode into a new UCS4 buffer that is allocated using PyMem_Malloc(). If this fails, NULL is returned with a MemoryError set. The returned buffer always has an extra null code point appended.

Added in version 3.3.

Locale Encoding

The current locale encoding can be used to decode text from the operating system.

PyObject *PyUnicode_DecodeLocaleAndSize(const char *str, Py_ssize_t length, const char *errors)

Return value: New reference. Part of the Stable ABI since version 3.7.

Decode a string from UTF-8 on Android and VxWorks, or from the current locale encoding on other platforms. The supported error handlers are "strict" and "surrogateescape" (PEP 383). The decoder uses "strict" error handler if errors is NULL. str must end with a null character but cannot contain embedded null characters.

Use PyUnicode_DecodeFSDefaultAndSize() to decode a string from the filesystem encoding and error handler.

This function ignores the Python UTF-8 Mode.

See also

The Py_DecodeLocale() function.

Added in version 3.3.

Changed in version 3.7: The function now also uses the current locale encoding for the surrogateescape error handler, except on Android. Previously, Py_DecodeLocale() was used for the surrogateescape, and the current locale encoding was used for strict.

PyObject *PyUnicode_DecodeLocale(const char *str, const char *errors)

Return value: New reference. Part of the Stable ABI since version 3.7.

Similar to PyUnicode_DecodeLocaleAndSize(), but compute the string length using strlen().

Added in version 3.3.

PyObject *PyUnicode_EncodeLocale(PyObject *unicode, const char *errors)

Return value: New reference. Part of the Stable ABI since version 3.7.

Encode a Unicode object to UTF-8 on Android and VxWorks, or to the current locale encoding on other platforms. The supported error handlers are "strict" and "surrogateescape" (PEP 383). The encoder uses "strict" error handler if errors is NULL. Return a bytes object. unicode cannot contain embedded null characters.

Use PyUnicode_EncodeFSDefault() to encode a string to the filesystem encoding and error handler.

This function ignores the Python UTF-8 Mode.

See also

The Py_EncodeLocale() function.

Added in version 3.3.

Changed in version 3.7: The function now also uses the current locale encoding for the surrogateescape error handler, except on Android. Previously, Py_EncodeLocale() was used for the surrogateescape, and the current locale encoding was used for strict.

File System Encoding

Functions encoding to and decoding from the filesystem encoding and error handler (PEP 383 and PEP 529).

To encode file names to bytes during argument parsing, the "O&" converter should be used, passing PyUnicode_FSConverter() as the conversion function:

int PyUnicode_FSConverter(PyObject *obj, void *result)

Part of the Stable ABI.

ParseTuple converter: encode str objects – obtained directly or through the os.PathLike interface – to bytes using PyUnicode_EncodeFSDefault(); bytes objects are output as-is. result must be a PyBytesObject* which must be released when it is no longer used.

Added in version 3.1.

Changed in version 3.6: Accepts a path-like object.

To decode file names to str during argument parsing, the "O&" converter should be used, passing PyUnicode_FSDecoder() as the conversion function:

int PyUnicode_FSDecoder(PyObject *obj, void *result)

Part of the Stable ABI.

ParseTuple converter: decode bytes objects – obtained either directly or indirectly through the os.PathLike interface – to str using PyUnicode_DecodeFSDefaultAndSize(); str objects are output as-is. result must be a PyUnicodeObject* which must be released when it is no longer used.

Added in version 3.2.

Changed in version 3.6: Accepts a path-like object.

PyObject *PyUnicode_DecodeFSDefaultAndSize(const char *str, Py_ssize_t size)

Return value: New reference. Part of the Stable ABI.

Decode a string from the filesystem encoding and error handler.

If you need to decode a string from the current locale encoding, use PyUnicode_DecodeLocaleAndSize().

See also

The Py_DecodeLocale() function.

Changed in version 3.6: The filesystem error handler is now used.

PyObject *PyUnicode_DecodeFSDefault(const char *str)

Return value: New reference. Part of the Stable ABI.

Decode a null-terminated string from the filesystem encoding and error handler.

If the string length is known, use PyUnicode_DecodeFSDefaultAndSize().

Changed in version 3.6: The filesystem error handler is now used.

PyObject *PyUnicode_EncodeFSDefault(PyObject *unicode)

Return value: New reference. Part of the Stable ABI.

Encode a Unicode object to the filesystem encoding and error handler, and return bytes. Note that the resulting bytes object can contain null bytes.

If you need to encode a string to the current locale encoding, use PyUnicode_EncodeLocale().

See also

The Py_EncodeLocale() function.

Added in version 3.2.

Changed in version 3.6: The filesystem error handler is now used.

wchar_t Support

wchar_t support for platforms which support it:

PyObject *PyUnicode_FromWideChar(const wchar_t *wstr, Py_ssize_t size)

Return value: New reference. Part of the Stable ABI.

Create a Unicode object from the wchar_t buffer wstr of the given size. Passing -1 as the size indicates that the function must itself compute the length, using wcslen(). Return NULL on failure.

Py_ssize_t PyUnicode_AsWideChar(PyObject *unicode, wchar_t *wstr, Py_ssize_t size)

Part of the Stable ABI.

Copy the Unicode object contents into the wchar_t buffer wstr. At most size wchar_t characters are copied (excluding a possibly trailing null termination character). Return the number of wchar_t characters copied or -1 in case of an error.

When wstr is NULL, instead return the size that would be required to store all of unicode including a terminating null.

Note that the resulting wchar_t* string may or may not be null-terminated. It is the responsibility of the caller to make sure that the wchar_t* string is null-terminated in case this is required by the application. Also, note that the wchar_t* string might contain null characters, which would cause the string to be truncated when used with most C functions.

wchar_t *PyUnicode_AsWideCharString(PyObject *unicode, Py_ssize_t *size)

Part of the Stable ABI since version 3.7.

Convert the Unicode object to a wide character string. The output string always ends with a null character. If size is not NULL, write the number of wide characters (excluding the trailing null termination character) into *size. Note that the resulting wchar_t string might contain null characters, which would cause the string to be truncated when used with most C functions. If size is NULL and the wchar_t* string contains null characters a ValueError is raised.

Returns a buffer allocated by PyMem_New (use PyMem_Free() to free it) on success. On error, returns NULL and *size is undefined. Raises a MemoryError if memory allocation is failed.

Added in version 3.2.

Changed in version 3.7: Raises a ValueError if size is NULL and the wchar_t* string contains null characters.

Built-in Codecs

Python provides a set of built-in 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, and they have the same semantics as the ones of the built-in str() string object constructor.

Setting encoding to NULL causes the default encoding to be used which is UTF-8. The file system calls should use PyUnicode_FSConverter() for encoding file names. This uses the filesystem encoding and error handler internally.

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 built-in codecs is “strict” (ValueError is raised).

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

Generic Codecs

These are the generic codec APIs:

PyObject *PyUnicode_Decode(const char *str, Py_ssize_t size, const char *encoding, const char *errors)

Return value: New reference. Part of the Stable ABI.

Create a Unicode object by decoding size bytes of the encoded string str. encoding and errors have the same meaning as the parameters of the same name in the str() built-in 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_AsEncodedString(PyObject *unicode, const char *encoding, const char *errors)

Return value: New reference. Part of the Stable ABI.

Encode a Unicode object and return the result as Python bytes 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.

UTF-8 Codecs

These are the UTF-8 codec APIs:

PyObject *PyUnicode_DecodeUTF8(const char *str, Py_ssize_t size, const char *errors)

Return value: New reference. Part of the Stable ABI.

Create a Unicode object by decoding size bytes of the UTF-8 encoded string str. Return NULL if an exception was raised by the codec.

PyObject *PyUnicode_DecodeUTF8Stateful(const char *str, Py_ssize_t size, const char *errors, Py_ssize_t *consumed)

Return value: New reference. Part of the Stable ABI.

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.

PyObject *PyUnicode_AsUTF8String(PyObject *unicode)

Return value: New reference. Part of the Stable ABI.

Encode a Unicode object using UTF-8 and return the result as Python bytes object. Error handling is “strict”. Return NULL if an exception was raised by the codec.

The function fails if the string contains surrogate code points (U+D800 - U+DFFF).

const char *PyUnicode_AsUTF8AndSize(PyObject *unicode, Py_ssize_t *size)

Part of the Stable ABI since version 3.10.

Return a pointer to the UTF-8 encoding of the Unicode object, and store the size of the encoded representation (in bytes) in size. The size argument can be NULL; in this case no size will be stored. The returned buffer always has an extra null byte appended (not included in size), regardless of whether there are any other null code points.

On error, set an exception, set size to -1 (if it’s not NULL) and return NULL.

The function fails if the string contains surrogate code points (U+D800 - U+DFFF).

This caches the UTF-8 representation of the string in the Unicode object, and subsequent calls will return a pointer to the same buffer. The caller is not responsible for deallocating the buffer. The buffer is deallocated and pointers to it become invalid when the Unicode object is garbage collected.

Added in version 3.3.

Changed in version 3.7: The return type is now const char * rather of char *.

Changed in version 3.10: This function is a part of the limited API.

const char *PyUnicode_AsUTF8(PyObject *unicode)

As PyUnicode_AsUTF8AndSize(), but does not store the size.

Added in version 3.3.

Changed in version 3.7: The return type is now const char * rather of char *.

UTF-32 Codecs

These are the UTF-32 codec APIs:

PyObject *PyUnicode_DecodeUTF32(const char *str, Py_ssize_t size, const char *errors, int *byteorder)

Return value: New reference. Part of the Stable ABI.

Decode size 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

If *byteorder is zero, and the first four bytes of the input data are a byte order mark (BOM), the decoder switches to this byte order and the BOM is not copied into the resulting Unicode string. If *byteorder is -1 or 1, any byte order mark is copied to the output.

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_DecodeUTF32Stateful(const char *str, Py_ssize_t size, const char *errors, int *byteorder, Py_ssize_t *consumed)

Return value: New reference. Part of the Stable ABI.

If consumed is NULL, behave like PyUnicode_DecodeUTF32(). If consumed is not NULL, 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.

PyObject *PyUnicode_AsUTF32String(PyObject *unicode)

Return value: New reference. Part of the Stable ABI.

Return a Python byte 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.

UTF-16 Codecs

These are the UTF-16 codec APIs:

PyObject *PyUnicode_DecodeUTF16(const char *str, Py_ssize_t size, const char *errors, int *byteorder)

Return value: New reference. Part of the Stable ABI.

Decode size 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

If *byteorder is zero, and the first two bytes of the input data are a byte order mark (BOM), the decoder switches to this byte order and the BOM is not copied into the resulting Unicode string. If *byteorder is -1 or 1, any byte order mark is copied to the output (where it will result in either a \ufeff or a \ufffe character).

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 *str, Py_ssize_t size, const char *errors, int *byteorder, Py_ssize_t *consumed)

Return value: New reference. Part of the Stable ABI.

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.

PyObject *PyUnicode_AsUTF16String(PyObject *unicode)

Return value: New reference. Part of the Stable ABI.

Return a Python byte 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.

UTF-7 Codecs

These are the UTF-7 codec APIs:

PyObject *PyUnicode_DecodeUTF7(const char *str, Py_ssize_t size, const char *errors)

Return value: New reference. Part of the Stable ABI.

Create a Unicode object by decoding size bytes of the UTF-7 encoded string str. Return NULL if an exception was raised by the codec.

PyObject *PyUnicode_DecodeUTF7Stateful(const char *str, Py_ssize_t size, const char *errors, Py_ssize_t *consumed)

Return value: New reference. Part of the Stable ABI.

If consumed is NULL, behave like PyUnicode_DecodeUTF7(). If consumed is not NULL, trailing incomplete UTF-7 base-64 sections 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.

Unicode-Escape Codecs

These are the “Unicode Escape” codec APIs:

PyObject *PyUnicode_DecodeUnicodeEscape(const char *str, Py_ssize_t size, const char *errors)

Return value: New reference. Part of the Stable ABI.

Create a Unicode object by decoding size bytes of the Unicode-Escape encoded string str. Return NULL if an exception was raised by the codec.

PyObject *PyUnicode_AsUnicodeEscapeString(PyObject *unicode)

Return value: New reference. Part of the Stable ABI.

Encode a Unicode object using Unicode-Escape and return the result as a bytes object. Error handling is “strict”. Return NULL if an exception was raised by the codec.

Raw-Unicode-Escape Codecs

These are the “Raw Unicode Escape” codec APIs:

PyObject *PyUnicode_DecodeRawUnicodeEscape(const char *str, Py_ssize_t size, const char *errors)

Return value: New reference. Part of the Stable ABI.

Create a Unicode object by decoding size bytes of the Raw-Unicode-Escape encoded string str. Return NULL if an exception was raised by the codec.

PyObject *PyUnicode_AsRawUnicodeEscapeString(PyObject *unicode)

Return value: New reference. Part of the Stable ABI.

Encode a Unicode object using Raw-Unicode-Escape and return the result as a bytes object. Error handling is “strict”. Return NULL if an exception was raised by the codec.

Latin-1 Codecs

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 *str, Py_ssize_t size, const char *errors)

Return value: New reference. Part of the Stable ABI.

Create a Unicode object by decoding size bytes of the Latin-1 encoded string str. Return NULL if an exception was raised by the codec.

PyObject *PyUnicode_AsLatin1String(PyObject *unicode)

Return value: New reference. Part of the Stable ABI.

Encode a Unicode object using Latin-1 and return the result as Python bytes object. Error handling is “strict”. Return NULL if an exception was raised by the codec.

ASCII Codecs

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

PyObject *PyUnicode_DecodeASCII(const char *str, Py_ssize_t size, const char *errors)

Return value: New reference. Part of the Stable ABI.

Create a Unicode object by decoding size bytes of the ASCII encoded string str. Return NULL if an exception was raised by the codec.

PyObject *PyUnicode_AsASCIIString(PyObject *unicode)

Return value: New reference. Part of the Stable ABI.

Encode a Unicode object using ASCII and return the result as Python bytes object. Error handling is “strict”. Return NULL if an exception was raised by the codec.

Character Map Codecs

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 mappings to encode and decode characters. The mapping objects provided must support the __getitem__() mapping interface; dictionaries and sequences work well.

These are the mapping codec APIs:

PyObject *PyUnicode_DecodeCharmap(const char *str, Py_ssize_t length, PyObject *mapping, const char *errors)

Return value: New reference. Part of the Stable ABI.

Create a Unicode object by decoding size bytes of the encoded string str using the given mapping object. Return NULL if an exception was raised by the codec.

If mapping is NULL, Latin-1 decoding will be applied. Else mapping must map bytes ordinals (integers in the range from 0 to 255) to Unicode strings, integers (which are then interpreted as Unicode ordinals) or None. Unmapped data bytes – ones which cause a LookupError, as well as ones which get mapped to None, 0xFFFE or '\ufffe', are treated as undefined mappings and cause an error.

PyObject *PyUnicode_AsCharmapString(PyObject *unicode, PyObject *mapping)

Return value: New reference. Part of the Stable ABI.

Encode a Unicode object using the given mapping object and return the result as a bytes object. Error handling is “strict”. Return NULL if an exception was raised by the codec.

The mapping object must map Unicode ordinal integers to bytes objects, integers in the range from 0 to 255 or None. Unmapped character ordinals (ones which cause a LookupError) as well as mapped to None are treated as “undefined mapping” and cause an error.

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

PyObject *PyUnicode_Translate(PyObject *unicode, PyObject *table, const char *errors)

Return value: New reference. Part of the Stable ABI.

Translate a string by applying a character mapping table to it and return the resulting Unicode object. Return NULL if 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.

errors has the usual meaning for codecs. It may be NULL which indicates to use the default error handling.

MBCS codecs for Windows

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 *str, Py_ssize_t size, const char *errors)

Return value: New reference. Part of the Stable ABI on Windows since version 3.7.

Create a Unicode object by decoding size bytes of the MBCS encoded string str. Return NULL if an exception was raised by the codec.

PyObject *PyUnicode_DecodeMBCSStateful(const char *str, Py_ssize_t size, const char *errors, Py_ssize_t *consumed)

Return value: New reference. Part of the Stable ABI on Windows since version 3.7.

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.

PyObject *PyUnicode_AsMBCSString(PyObject *unicode)

Return value: New reference. Part of the Stable ABI on Windows since version 3.7.

Encode a Unicode object using MBCS and return the result as Python bytes object. Error handling is “strict”. Return NULL if an exception was raised by the codec.

PyObject *PyUnicode_EncodeCodePage(int code_page, PyObject *unicode, const char *errors)

Return value: New reference. Part of the Stable ABI on Windows since version 3.7.

Encode the Unicode object using the specified code page and return a Python bytes object. Return NULL if an exception was raised by the codec. Use CP_ACP code page to get the MBCS encoder.

Added in version 3.3.

Methods & Slots

Methods and Slot Functions

The following APIs are capable of handling Unicode objects and strings on input (we refer to them as strings in the descriptions) and return Unicode objects or integers as appropriate.

They all return NULL or -1 if an exception occurs.

PyObject *PyUnicode_Concat(PyObject *left, PyObject *right)

Return value: New reference. Part of the Stable ABI.

Concat two strings giving a new Unicode string.

PyObject *PyUnicode_Split(PyObject *unicode, PyObject *sep, Py_ssize_t maxsplit)

Return value: New reference. Part of the Stable ABI.

Split a string giving a list of Unicode strings. If sep is NULL, splitting will be done at all whitespace substrings. Otherwise, splits occur at the given separator. At most maxsplit splits will be done. If negative, no limit is set. Separators are not included in the resulting list.

PyObject *PyUnicode_Splitlines(PyObject *unicode, int keepends)

Return value: New reference. Part of the Stable ABI.

Split a Unicode string at line breaks, returning a list of Unicode strings. CRLF is considered to be one line break. If keepends is 0, the Line break characters are not included in the resulting strings.

PyObject *PyUnicode_Join(PyObject *separator, PyObject *seq)

Return value: New reference. Part of the Stable ABI.

Join a sequence of strings using the given separator and return the resulting Unicode string.

Py_ssize_t PyUnicode_Tailmatch(PyObject *unicode, PyObject *substr, Py_ssize_t start, Py_ssize_t end, int direction)

Part of the Stable ABI.

Return 1 if substr matches unicode[start:end] at the given tail end (direction == -1 means to do a prefix match, direction == 1 a suffix match), 0 otherwise. Return -1 if an error occurred.

Py_ssize_t PyUnicode_Find(PyObject *unicode, PyObject *substr, Py_ssize_t start, Py_ssize_t end, int direction)

Part of the Stable ABI.

Return the first position of substr in unicode[start:end] using the given direction (direction == 1 means to do a forward search, direction == -1 a backward search). The return value is the index of the first match; a value of -1 indicates that no match was found, and -2 indicates that an error occurred and an exception has been set.

Py_ssize_t PyUnicode_FindChar(PyObject *unicode, Py_UCS4 ch, Py_ssize_t start, Py_ssize_t end, int direction)

Part of the Stable ABI since version 3.7.

Return the first position of the character ch in unicode[start:end] using the given direction (direction == 1 means to do a forward search, direction == -1 a backward search). The return value is the index of the first match; a value of -1 indicates that no match was found, and -2 indicates that an error occurred and an exception has been set.

Added in version 3.3.

Changed in version 3.7: start and end are now adjusted to behave like unicode[start:end].

Py_ssize_t PyUnicode_Count(PyObject *unicode, PyObject *substr, Py_ssize_t start, Py_ssize_t end)

Part of the Stable ABI.

Return the number of non-overlapping occurrences of substr in unicode[start:end]. Return -1 if an error occurred.

PyObject *PyUnicode_Replace(PyObject *unicode, PyObject *substr, PyObject *replstr, Py_ssize_t maxcount)

Return value: New reference. Part of the Stable ABI.

Replace at most maxcount occurrences of substr in unicode with replstr and return the resulting Unicode object. maxcount == -1 means replace all occurrences.

int PyUnicode_Compare(PyObject *left, PyObject *right)

Part of the Stable ABI.

Compare two strings and return -1, 0, 1 for less than, equal, and greater than, respectively.

This function returns -1 upon failure, so one should call PyErr_Occurred() to check for errors.

int PyUnicode_EqualToUTF8AndSize(PyObject *unicode, const char *string, Py_ssize_t size)

Part of the Stable ABI since version 3.13.

Compare a Unicode object with a char buffer which is interpreted as being UTF-8 or ASCII encoded and return true (1) if they are equal, or false (0) otherwise. If the Unicode object contains surrogate code points (U+D800 - U+DFFF) or the C string is not valid UTF-8, false (0) is returned.

This function does not raise exceptions.

Added in version 3.13.

int PyUnicode_EqualToUTF8(PyObject *unicode, const char *string)

Part of the Stable ABI since version 3.13.

Similar to PyUnicode_EqualToUTF8AndSize(), but compute string length using strlen(). If the Unicode object contains null characters, false (0) is returned.

Added in version 3.13.

int PyUnicode_CompareWithASCIIString(PyObject *unicode, const char *string)

Part of the Stable ABI.

Compare a Unicode object, unicode, with string and return -1, 0, 1 for less than, equal, and greater than, respectively. It is best to pass only ASCII-encoded strings, but the function interprets the input string as ISO-8859-1 if it contains non-ASCII characters.

This function does not raise exceptions.

PyObject *PyUnicode_RichCompare(PyObject *left, PyObject *right, int op)

Return value: New reference. Part of the Stable ABI.

Rich compare two Unicode strings and return one of the following:

• NULL in case an exception was raised

• Py_True or Py_False for successful comparisons

• Py_NotImplemented in case the type combination is unknown

Possible values for op are Py_GT, Py_GE, Py_EQ, Py_NE, Py_LT, and Py_LE.

PyObject *PyUnicode_Format(PyObject *format, PyObject *args)

Return value: New reference. Part of the Stable ABI.

Return a new string object from format and args; this is analogous to format % args.

int PyUnicode_Contains(PyObject *unicode, PyObject *substr)

Part of the Stable ABI.

Check whether substr is contained in unicode and return true or false accordingly.

substr has to coerce to a one element Unicode string. -1 is returned if there was an error.

void PyUnicode_InternInPlace(PyObject **p_unicode)

Part of the Stable ABI.

Intern the argument *p_unicode in place. The argument must be the address of a pointer variable pointing to a Python Unicode string object. If there is an existing interned string that is the same as *p_unicode, it sets *p_unicode to it (releasing the reference to the old string object and creating a new strong reference to the interned string object), otherwise it leaves *p_unicode alone and interns it.

(Clarification: even though there is a lot of talk about references, think of this function as reference-neutral. You must own the object you pass in; after the call you no longer own the passed-in reference, but you newly own the result.)

This function never raises an exception. On error, it leaves its argument unchanged without interning it.

Instances of subclasses of str may not be interned, that is, PyUnicode_CheckExact(*p_unicode) must be true. If it is not, then – as with any other error – the argument is left unchanged.

Note that interned strings are not “immortal”. You must keep a reference to the result to benefit from interning.

PyObject *PyUnicode_InternFromString(const char *str)

Return value: New reference. Part of the Stable ABI.

A combination of PyUnicode_FromString() and PyUnicode_InternInPlace(), meant for statically allocated strings.

Return a new (“owned”) reference to either a new Unicode string object that has been interned, or an earlier interned string object with the same value.

Python may keep a reference to the result, or make it immortal, preventing it from being garbage-collected promptly. For interning an unbounded number of different strings, such as ones coming from user input, prefer calling PyUnicode_FromString() and PyUnicode_InternInPlace() directly.

CPython implementation detail: Strings interned this way are made immortal.