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).

Py_UNICODE* and UTF-8 representations are created on demand and cached in the Unicode object. The Py_UNICODE* representation is deprecated and inefficient; it should be avoided in performance- or memory-sensitive situations.

Due to the transition between the old APIs and the new APIs, unicode objects can internally be in two states depending on how they were created:

  • “canonical” unicode objects are all objects created by a non-deprecated unicode API. They use the most efficient representation allowed by the implementation.
  • “legacy” unicode objects have been created through one of the deprecated APIs (typically PyUnicode_FromUnicode()) and only bear the Py_UNICODE* representation; you will have to call PyUnicode_READY() on them before calling any other API.

Unicode Type

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

Py_UCS4
Py_UCS2
Py_UCS1

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.

New in version 3.3.

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.

PyASCIIObject
PyCompactUnicodeObject
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.

New in version 3.3.

PyTypeObject PyUnicode_Type

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

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:

int PyUnicode_Check(PyObject *o)

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

int PyUnicode_CheckExact(PyObject *o)

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

int PyUnicode_READY(PyObject *o)

Ensure the string object o is in the “canonical” representation. This is required before using any of the access macros described below.

Returns 0 on success and -1 with an exception set on failure, which in particular happens if memory allocation fails.

New in version 3.3.

Py_ssize_t PyUnicode_GET_LENGTH(PyObject *o)

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

New in version 3.3.

Py_UCS1* PyUnicode_1BYTE_DATA(PyObject *o)
Py_UCS2* PyUnicode_2BYTE_DATA(PyObject *o)
Py_UCS4* PyUnicode_4BYTE_DATA(PyObject *o)

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 macro. Make sure PyUnicode_READY() has been called before accessing this.

New in version 3.3.

PyUnicode_WCHAR_KIND
PyUnicode_1BYTE_KIND
PyUnicode_2BYTE_KIND
PyUnicode_4BYTE_KIND

Return values of the PyUnicode_KIND() macro.

New in version 3.3.

int PyUnicode_KIND(PyObject *o)

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

New in version 3.3.

void* PyUnicode_DATA(PyObject *o)

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

New 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 macro does not do any sanity checks and is intended for usage in loops. The caller should cache the kind value and data pointer as obtained from other macro 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.

New 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.

New in version 3.3.

Py_UCS4 PyUnicode_READ_CHAR(PyObject *o, Py_ssize_t index)

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

New in version 3.3.

PyUnicode_MAX_CHAR_VALUE(PyObject *o)

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

New in version 3.3.

int PyUnicode_ClearFreeList()

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

Py_ssize_t PyUnicode_GET_SIZE(PyObject *o)

Return the size of the deprecated Py_UNICODE representation, in code units (this includes surrogate pairs as 2 units). o has to be a Unicode object (not checked).

Part of the old-style Unicode API, please migrate to using PyUnicode_GET_LENGTH().

Deprecated since version 3.3, will be removed in version 4.0.

Py_ssize_t PyUnicode_GET_DATA_SIZE(PyObject *o)

Return the size of the deprecated Py_UNICODE representation in bytes. o has to be a Unicode object (not checked).

Part of the old-style Unicode API, please migrate to using PyUnicode_GET_LENGTH().

Deprecated since version 3.3, will be removed in version 4.0.

Py_UNICODE* PyUnicode_AS_UNICODE(PyObject *o)
const char* PyUnicode_AS_DATA(PyObject *o)

Return a pointer to a Py_UNICODE representation of the object. The AS_DATA form casts the pointer to const char *. o has to be a Unicode object (not checked).

Changed in version 3.3: This macro is now inefficient – because in many cases the Py_UNICODE representation does not exist and needs to be created – and can fail (return NULL with an exception set). Try to port the code to use the new PyUnicode_nBYTE_DATA() macros or use PyUnicode_WRITE() or PyUnicode_READ().

Part of the old-style Unicode API, please migrate to using the PyUnicode_nBYTE_DATA() family of macros.

Deprecated since version 3.3, will be removed in version 4.0.

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_UNICODE ch)

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

int Py_UNICODE_ISLOWER(Py_UNICODE ch)

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

int Py_UNICODE_ISUPPER(Py_UNICODE ch)

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

int Py_UNICODE_ISTITLE(Py_UNICODE ch)

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

int Py_UNICODE_ISLINEBREAK(Py_UNICODE ch)

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

int Py_UNICODE_ISDECIMAL(Py_UNICODE ch)

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

int Py_UNICODE_ISDIGIT(Py_UNICODE ch)

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

int Py_UNICODE_ISNUMERIC(Py_UNICODE ch)

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

int Py_UNICODE_ISALPHA(Py_UNICODE ch)

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

int Py_UNICODE_ISALNUM(Py_UNICODE ch)

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

int Py_UNICODE_ISPRINTABLE(Py_UNICODE 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_UNICODE Py_UNICODE_TOLOWER(Py_UNICODE ch)

Return the character ch converted to lower case.

Deprecated since version 3.3: This function uses simple case mappings.

Py_UNICODE Py_UNICODE_TOUPPER(Py_UNICODE ch)

Return the character ch converted to upper case.

Deprecated since version 3.3: This function uses simple case mappings.

Py_UNICODE Py_UNICODE_TOTITLE(Py_UNICODE ch)

Return the character ch converted to title case.

Deprecated since version 3.3: This function uses simple case mappings.

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.

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.

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.

These APIs can be used to work with surrogates:

Py_UNICODE_IS_SURROGATE(ch)

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

Py_UNICODE_IS_HIGH_SURROGATE(ch)

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

Py_UNICODE_IS_LOW_SURROGATE(ch)

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

Py_UNICODE_JOIN_SURROGATES(high, low)

Join two surrogate characters and return a single Py_UCS4 value. high and low are respectively the leading and trailing surrogates in a surrogate pair.

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)

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.

New in version 3.3.

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

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.

New in version 3.3.

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

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

If u is NULL, this function behaves like PyUnicode_FromUnicode() with the buffer set to NULL. This usage is deprecated in favor of PyUnicode_New().

PyObject *PyUnicode_FromString(const char *u)

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

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

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. The following format characters are allowed:

Format Characters Type Comment
%% n/a The literal % character.
%c int A single character, represented as an C int.
%d int Exactly equivalent to printf("%d").
%u unsigned int Exactly equivalent to printf("%u").
%ld long Exactly equivalent to printf("%ld").
%li long Exactly equivalent to printf("%li").
%lu unsigned long Exactly equivalent to printf("%lu").
%lld long long Exactly equivalent to printf("%lld").
%lli long long Exactly equivalent to printf("%lli").
%llu unsigned long long Exactly equivalent to printf("%llu").
%zd Py_ssize_t Exactly equivalent to printf("%zd").
%zi Py_ssize_t Exactly equivalent to printf("%zi").
%zu size_t Exactly equivalent to printf("%zu").
%i int Exactly equivalent to printf("%i").
%x int Exactly equivalent to printf("%x").
%s char* A null-terminated C character array.
%p 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*, char * 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().

An unrecognized format character causes all the rest of the format string to be copied as-is to the result string, and any extra arguments discarded.

Note

The “%lld” and “%llu” format specifiers are only available when HAVE_LONG_LONG is defined.

Note

The width formatter unit is number of characters rather than bytes. The precision formatter unit is number of bytes 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).

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.

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

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

PyObject* PyUnicode_FromEncodedObject(PyObject *obj, const char *encoding, const char *errors)
Return value: New reference.

Coerce an encoded object obj to an Unicode object and return a reference with incremented refcount.

bytes, bytearray 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 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)

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

New in version 3.3.

int 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 0.

New 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.

New in version 3.3.

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

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), in contrast to the macro version PyUnicode_WRITE_CHAR().

New in version 3.3.

Py_UCS4 PyUnicode_ReadChar(PyObject *unicode, Py_ssize_t index)

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 the macro version PyUnicode_READ_CHAR().

New in version 3.3.

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

Return a substring of str, from character index start (included) to character index end (excluded). Negative indices are not supported.

New in version 3.3.

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

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

New in version 3.3.

Py_UCS4* PyUnicode_AsUCS4Copy(PyObject *u)

Copy the string u into a new UCS4 buffer that is allocated using PyMem_Malloc(). If this fails, NULL is returned with a MemoryError set.

New in version 3.3.

Deprecated Py_UNICODE APIs

Deprecated since version 3.3, will be removed in version 4.0.

These API functions are deprecated with the implementation of PEP 393. Extension modules can continue using them, as they will not be removed in Python 3.x, but need to be aware that their use can now cause performance and memory hits.

PyObject* PyUnicode_FromUnicode(const Py_UNICODE *u, Py_ssize_t size)
Return value: New reference.

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.

If the buffer is NULL, PyUnicode_READY() must be called once the string content has been filled before using any of the access macros such as PyUnicode_KIND().

Please migrate to using PyUnicode_FromKindAndData() or PyUnicode_New().

Py_UNICODE* PyUnicode_AsUnicode(PyObject *unicode)

Return a read-only pointer to the Unicode object’s internal Py_UNICODE buffer, or NULL on error. This will create the Py_UNICODE* representation of the object if it is not yet available. Note that the resulting Py_UNICODE string may contain embedded null characters, which would cause the string to be truncated when used in most C functions.

Please migrate to using PyUnicode_AsUCS4(), PyUnicode_Substring(), PyUnicode_ReadChar() or similar new APIs.

PyObject* PyUnicode_TransformDecimalToASCII(Py_UNICODE *s, Py_ssize_t size)

Create a Unicode object by replacing all decimal digits in Py_UNICODE buffer of the given size by ASCII digits 0–9 according to their decimal value. Return NULL if an exception occurs.

Py_UNICODE* PyUnicode_AsUnicodeAndSize(PyObject *unicode, Py_ssize_t *size)

Like PyUnicode_AsUnicode(), but also saves the Py_UNICODE() array length in size. Note that the resulting Py_UNICODE* string may contain embedded null characters, which would cause the string to be truncated when used in most C functions.

New in version 3.3.

Py_UNICODE* PyUnicode_AsUnicodeCopy(PyObject *unicode)

Create a copy of a Unicode string ending with a nul character. Return NULL and raise a MemoryError exception on memory allocation failure, otherwise return a new allocated buffer (use PyMem_Free() to free the buffer). Note that the resulting Py_UNICODE* string may contain embedded null characters, which would cause the string to be truncated when used in most C functions.

New in version 3.2.

Please migrate to using PyUnicode_AsUCS4Copy() or similar new APIs.

Py_ssize_t PyUnicode_GetSize(PyObject *unicode)

Return the size of the deprecated Py_UNICODE representation, in code units (this includes surrogate pairs as 2 units).

Please migrate to using PyUnicode_GetLength().

PyObject* PyUnicode_FromObject(PyObject *obj)
Return value: New reference.

Shortcut for PyUnicode_FromEncodedObject(obj, NULL, "strict") which is used throughout the interpreter whenever coercion to Unicode is needed.

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 len, const char *errors)

Decode a string from the current locale encoding. 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.

See also

Use PyUnicode_DecodeFSDefaultAndSize() to decode a string from Py_FileSystemDefaultEncoding (the locale encoding read at Python startup).

New in version 3.3.

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

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

New in version 3.3.

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

Encode a Unicode object to the current locale encoding. The supported error handlers are "strict" and "surrogateescape" (PEP 383). The encoder uses "strict" error handler if errors is NULL. Return a bytes object. str cannot contain embedded null characters.

See also

Use PyUnicode_EncodeFSDefault() to encode a string to Py_FileSystemDefaultEncoding (the locale encoding read at Python startup).

New in version 3.3.

File System Encoding

To encode and decode file names and other environment strings, Py_FileSystemEncoding should be used as the encoding, and "surrogateescape" should be used as the error handler (PEP 383). To encode file names during argument parsing, the "O&" converter should be used, passing PyUnicode_FSConverter() as the conversion function:

int PyUnicode_FSConverter(PyObject* obj, void* result)

ParseTuple converter: encode str objects 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.

New in version 3.1.

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

int PyUnicode_FSDecoder(PyObject* obj, void* result)

ParseTuple converter: decode bytes objects 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.

New in version 3.2.

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

Decode a string using Py_FileSystemDefaultEncoding and the "surrogateescape" error handler, or "strict" on Windows.

If Py_FileSystemDefaultEncoding is not set, fall back to the locale encoding.

See also

Py_FileSystemDefaultEncoding is initialized at startup from the locale encoding and cannot be modified later. If you need to decode a string from the current locale encoding, use PyUnicode_DecodeLocaleAndSize().

Changed in version 3.2: Use "strict" error handler on Windows.

PyObject* PyUnicode_DecodeFSDefault(const char *s)

Decode a null-terminated string using Py_FileSystemDefaultEncoding and the "surrogateescape" error handler, or "strict" on Windows.

If Py_FileSystemDefaultEncoding is not set, fall back to the locale encoding.

Use PyUnicode_DecodeFSDefaultAndSize() if you know the string length.

Changed in version 3.2: Use "strict" error handler on Windows.

PyObject* PyUnicode_EncodeFSDefault(PyObject *unicode)

Encode a Unicode object to Py_FileSystemDefaultEncoding with the "surrogateescape" error handler, or "strict" on Windows, and return bytes. Note that the resulting bytes object may contain null bytes.

If Py_FileSystemDefaultEncoding is not set, fall back to the locale encoding.

See also

Py_FileSystemDefaultEncoding is initialized at startup from the locale encoding and cannot be modified later. If you need to encode a string to the current locale encoding, use PyUnicode_EncodeLocale().

New in version 3.2.

wchar_t Support

wchar_t support for platforms which support it:

PyObject* PyUnicode_FromWideChar(const wchar_t *w, Py_ssize_t size)
Return value: New reference.

Create a Unicode object from the wchar_t buffer w 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(PyUnicodeObject *unicode, wchar_t *w, Py_ssize_t size)

Copy the Unicode object contents into the wchar_t buffer w. At most size wchar_t characters are copied (excluding a possibly trailing 0-termination character). Return the number of wchar_t characters copied or -1 in case of an error. Note that the resulting wchar_t* string may or may not be 0-terminated. It is the responsibility of the caller to make sure that the wchar_t* string is 0-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)

Convert the Unicode object to a wide character string. The output string always ends with a nul character. If size is not NULL, write the number of wide characters (excluding the trailing 0-termination character) into *size.

Returns a buffer allocated by PyMem_Alloc() (use PyMem_Free() to free it) on success. On error, returns NULL, *size is undefined and raises a MemoryError. 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.

New in version 3.2.

UCS4 Support

New in version 3.3.

size_t Py_UCS4_strlen(const Py_UCS4 *u)
Py_UCS4* Py_UCS4_strcpy(Py_UCS4 *s1, const Py_UCS4 *s2)
Py_UCS4* Py_UCS4_strncpy(Py_UCS4 *s1, const Py_UCS4 *s2, size_t n)
Py_UCS4* Py_UCS4_strcat(Py_UCS4 *s1, const Py_UCS4 *s2)
int Py_UCS4_strcmp(const Py_UCS4 *s1, const Py_UCS4 *s2)
int Py_UCS4_strncmp(const Py_UCS4 *s1, const Py_UCS4 *s2, size_t n)
Py_UCS4* Py_UCS4_strchr(const Py_UCS4 *s, Py_UCS4 c)
Py_UCS4* Py_UCS4_strrchr(const Py_UCS4 *s, Py_UCS4 c)

These utility functions work on strings of Py_UCS4 characters and otherwise behave like the C standard library functions with the same name.

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 ASCII. The file system calls should use PyUnicode_FSConverter() for encoding file names. This uses the variable Py_FileSystemDefaultEncoding internally. 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 built-in codecs is “strict” (ValueError is raised).

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

Generic Codecs

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 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.

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.

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 s of the given size and return a 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.

Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsEncodedString().

Deprecated since version 3.3, will be removed in version 4.0.

UTF-8 Codecs

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.

PyObject* PyUnicode_AsUTF8String(PyObject *unicode)
Return value: New reference.

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.

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

Return a pointer to the default encoding (UTF-8) of the Unicode object, and store the size of the encoded representation (in bytes) in size. size can be NULL, in this case no size will be stored.

In the case of an error, NULL is returned with an exception set and no size is stored.

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.

New in version 3.3.

char* PyUnicode_AsUTF8(PyObject *unicode)

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

New in version 3.3.

PyObject* PyUnicode_EncodeUTF8(const Py_UNICODE *s, Py_ssize_t size, const char *errors)
Return value: New reference.

Encode the Py_UNICODE buffer s of the given size using UTF-8 and return a Python bytes object. Return NULL if an exception was raised by the codec.

Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsUTF8String() or PyUnicode_AsUTF8AndSize().

Deprecated since version 3.3, will be removed in version 4.0.

UTF-32 Codecs

These are the UTF-32 codec APIs:

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

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

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 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.

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. 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.

Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsUTF32String().

Deprecated since version 3.3, will be removed in version 4.0.

UTF-16 Codecs

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 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 *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.

PyObject* PyUnicode_AsUTF16String(PyObject *unicode)
Return value: New reference.

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.

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

Return a Python bytes object holding the UTF-16 encoded value of the Unicode data in s. 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.

Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsUTF16String().

Deprecated since version 3.3, will be removed in version 4.0.

UTF-7 Codecs

These are the UTF-7 codec APIs:

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

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

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

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.

PyObject* PyUnicode_EncodeUTF7(const Py_UNICODE *s, Py_ssize_t size, int base64SetO, int base64WhiteSpace, const char *errors)

Encode the Py_UNICODE buffer of the given size using UTF-7 and return a Python bytes object. Return NULL if an exception was raised by the codec.

If base64SetO is nonzero, “Set O” (punctuation that has no otherwise special meaning) will be encoded in base-64. If base64WhiteSpace is nonzero, whitespace will be encoded in base-64. Both are set to zero for the Python “utf-7” codec.

Part of the old-style Py_UNICODE API.

Deprecated since version 3.3, will be removed in version 4.0.

Unicode-Escape Codecs

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_AsUnicodeEscapeString(PyObject *unicode)
Return value: New reference.

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.

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.

Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsUnicodeEscapeString().

Deprecated since version 3.3, will be removed in version 4.0.

Raw-Unicode-Escape Codecs

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_AsRawUnicodeEscapeString(PyObject *unicode)
Return value: New reference.

Encode a Unicode object 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.

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.

Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsRawUnicodeEscapeString().

Deprecated since version 3.3, will be removed in version 4.0.

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 *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_AsLatin1String(PyObject *unicode)
Return value: New reference.

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.

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 bytes object. Return NULL if an exception was raised by the codec.

Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsLatin1String().

Deprecated since version 3.3, will be removed in version 4.0.

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 *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_AsASCIIString(PyObject *unicode)
Return value: New reference.

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.

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 bytes object. Return NULL if an exception was raised by the codec.

Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsASCIIString().

Deprecated since version 3.3, will be removed in version 4.0.

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 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.

These are the mapping codec APIs:

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”.

PyObject* PyUnicode_AsCharmapString(PyObject *unicode, PyObject *mapping)
Return value: New reference.

Encode a Unicode object 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 size 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.

Part of the old-style Py_UNICODE API.

Deprecated since version 3.3, will be removed in version 4.0.

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.

Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsCharmapString().

Deprecated since version 3.3, will be removed in version 4.0.

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 *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.

PyObject* PyUnicode_AsMBCSString(PyObject *unicode)
Return value: New reference.

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)

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.

New in version 3.3.

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 bytes object. Return NULL if an exception was raised by the codec.

Part of the old-style Py_UNICODE API; please migrate to using PyUnicode_AsMBCSString() or PyUnicode_EncodeCodePage().

Deprecated since version 3.3, will be removed in version 4.0.

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.

Concat two strings giving a new Unicode string.

PyObject* PyUnicode_Split(PyObject *s, PyObject *sep, Py_ssize_t maxsplit)
Return value: New reference.

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 *s, int keepend)
Return value: New reference.

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

PyObject* PyUnicode_Translate(PyObject *str, PyObject *table, const char *errors)
Return value: New reference.

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

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.

PyObject* PyUnicode_Join(PyObject *separator, PyObject *seq)
Return value: New reference.

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

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

Return 1 if substr matches str[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 *str, PyObject *substr, Py_ssize_t start, Py_ssize_t end, int direction)

Return the first position of substr in str[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 *str, Py_UCS4 ch, Py_ssize_t start, Py_ssize_t end, int direction)

Return the first position of the character ch in str[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.

New in version 3.3.

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

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

PyObject* PyUnicode_Replace(PyObject *str, PyObject *substr, PyObject *replstr, Py_ssize_t maxcount)
Return value: New reference.

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

int PyUnicode_Compare(PyObject *left, PyObject *right)

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

int PyUnicode_CompareWithASCIIString(PyObject *uni, char *string)

Compare a unicode object, uni, 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”.

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

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

Note that Py_EQ and Py_NE comparisons can cause a UnicodeWarning in case the conversion of the arguments to Unicode fails with a UnicodeDecodeError.

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.

Return a new string object from format and args; this is analogous to format % args. The args argument must be a tuple.

int PyUnicode_Contains(PyObject *container, PyObject *element)

Check whether element is contained in container and return true or false accordingly.

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

void PyUnicode_InternInPlace(PyObject **string)

Intern the argument *string 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 *string, it sets *string to it (decrementing the reference count of the old string object and incrementing the reference count of the interned string object), otherwise it leaves *string alone and interns it (incrementing its reference count). (Clarification: even though there is a lot of talk about reference counts, think of this function as reference-count-neutral; you own the object after the call if and only if you owned it before the call.)

PyObject* PyUnicode_InternFromString(const char *v)

A combination of PyUnicode_FromString() and PyUnicode_InternInPlace(), returning either a new unicode string object that has been interned, or a new (“owned”) reference to an earlier interned string object with the same value.