# 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:

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`.

PyTypeObject PyUnicodeIter_Type
  Part of the Stable ABI.

  This instance of `PyTypeObject` represents the Python Unicode iterator type. It is used to iterate over Unicode string objects.

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 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.

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.

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 the code point value to the given zero-based index in a string.

  The kind value and data pointer must have been obtained from a string using `PyUnicode_KIND()` and `PyUnicode_DATA()` respectively. You must hold a reference to that string while calling `PyUnicode_WRITE()`. All requirements of `PyUnicode_WriteChar()` also apply.

  The function performs no checks for any of its requirements, and is intended for usage in loops.

  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 Names (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.

unsigned int PyUnicode_IS_ASCII(PyObject *unicode)

  Return true if the string only contains ASCII characters. Equivalent to `str.isascii()`.

  Added in version 3.2.

### 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, in the sense of `str.isprintable()`.

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_HIGH_SURROGATE(Py_UCS4 ch)

  Return the high UTF-16 surrogate (`0xD800` to `0xDBFF`) for a Unicode code point in the range `[0x10000; 0x10FFFF]`.

Py_UCS4 Py_UNICODE_LOW_SURROGATE(Py_UCS4 ch)

  Return the low UTF-16 surrogate (`0xDC00` to `0xDFFF`) for a Unicode code point in the range `[0x10000; 0x10FFFF]`.

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.

  On error, set an exception and return `NULL`.

  After creation, the string can be filled by `PyUnicode_WriteChar()`, `PyUnicode_CopyCharacters()`, `PyUnicode_Fill()`, `PyUnicode_WRITE()` or similar. Since strings are supposed to be immutable, take care to not “use” the result while it is being modified. In particular, before it’s filled with its final contents, a string:

  - must not be hashed,

  - must not be `converted to UTF-8`, or another non-“canonical” representation,

  - must not have its reference count changed,

  - must not be shared with code that might do one of the above.

  This list is not exhaustive. Avoiding these uses is your responsibility; Python does not always check these requirements.

  To avoid accidentally exposing a partially-written string object, prefer using the `PyUnicodeWriter` API, or one of the `PyUnicode_From*` functions below.

  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_FromOrdinal(int ordinal)
  Return value: New reference. Part of the Stable ABI.

  Create a Unicode Object from the given Unicode code point ordinal.

  The ordinal must be in `range(0x110000)`. A `ValueError` is raised in the case it is not.

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.

void PyUnicode_Append(PyObject **p_left, PyObject *right)
  Part of the Stable ABI.

  Append the string right to the end of p_left. p_left must point to a strong reference to a Unicode object; `PyUnicode_Append()` releases (“steals”) this reference.

  On error, set *p_left to `NULL` and set an exception.

  On success, set *p_left to a new strong reference to the result.

void PyUnicode_AppendAndDel(PyObject **p_left, PyObject *right)
  Part of the Stable ABI.

  The function is similar to `PyUnicode_Append()`, with the only difference being that it decrements the reference count of right by one.

PyObject *PyUnicode_BuildEncodingMap(PyObject *string)
  Return value: New reference. Part of the Stable ABI.

  Return a mapping suitable for decoding a custom single-byte encoding. Given a Unicode string string of up to 256 characters representing an encoding table, returns either a compact internal mapping object or a dictionary mapping character ordinals to byte values. Raises a `TypeError` and return `NULL` on invalid input.

  Added in version 3.2.

const char *PyUnicode_GetDefaultEncoding(void)
  Part of the Stable ABI.

  Return the name of the default string encoding, `"utf-8"`. See `sys.getdefaultencoding()`.

  The returned string does not need to be freed, and is valid until interpreter shutdown.

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.

  The string must not have been “used” yet. See `PyUnicode_New()` for details.

  Added in version 3.3.

int PyUnicode_Resize(PyObject **unicode, Py_ssize_t length);
  Part of the Stable ABI.

  Resize a Unicode object *unicode to the new length in code points.

  Try to resize the string in place (which is usually faster than allocating a new string and copying characters), or create a new string.

  *unicode is modified to point to the new (resized) object and `0` is returned on success. Otherwise, `-1` is returned and an exception is set, and *unicode is left untouched.

  The function doesn’t check string content, the result may not be a string in canonical representation.

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.

  The string must not have been “used” yet. See `PyUnicode_New()` for details.

  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 the string unicode at the zero-based index. Return `0` on success, `-1` on error with an exception set.

  This function checks that unicode is a Unicode object, that the index is not out of bounds, and that the object’s reference count is one. See `PyUnicode_WRITE()` for a version that skips these checks, making them your responsibility.

  The string must not have been “used” yet. See `PyUnicode_New()` for details.

  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.

  PyArg_Parse* 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 an address of a C variable of type PyObject* (or PyBytesObject*). On success, set the variable to a new strong reference to a bytes object which must be released when it is no longer used and return a non-zero value (`Py_CLEANUP_SUPPORTED`). Embedded null bytes are not allowed in the result. On failure, return `0` with an exception set.

  If obj is `NULL`, the function releases a strong reference stored in the variable referred by result and returns `1`.

  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.

  PyArg_Parse* 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 an address of a C variable of type PyObject* (or PyUnicodeObject*). On success, set the variable to a new strong reference to a Unicode object which must be released when it is no longer used and return a non-zero value (`Py_CLEANUP_SUPPORTED`). Embedded null characters are not allowed in the result. On failure, return `0` with an exception set.

  If obj is `NULL`, release the strong reference to the object referred to by result and return `1`.

  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

The following macro is provided:

Py_UNICODE_REPLACEMENT_CHARACTER

  The Unicode code point `U+FFFD` (replacement character).

  This Unicode character is used as the replacement character during decoding if the errors argument is set to “replace”.

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.

  Warning

  This function does not have any special behavior for null characters embedded within unicode. As a result, strings containing null characters will remain in the returned string, which some C functions might interpret as the end of the string, leading to truncation. If truncation is an issue, it is recommended to use `PyUnicode_AsUTF8AndSize()` instead.

  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_DecodeCodePageStateful(int code_page, 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.

  Similar to `PyUnicode_DecodeMBCSStateful()`, except uses the code page specified by code_page.

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 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.

  On error, return `NULL` with an exception set.

  Equivalent to `str.split()`.

PyObject *PyUnicode_RSplit(PyObject *unicode, PyObject *sep, Py_ssize_t maxsplit)
  Return value: New reference. Part of the Stable ABI.

  Similar to `PyUnicode_Split()`, but splitting will be done beginning at the end of the string.

  On error, return `NULL` with an exception set.

  Equivalent to `str.rsplit()`.

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_Partition(PyObject *unicode, PyObject *sep)
  Return value: New reference. Part of the Stable ABI.

  Split a Unicode string at the first occurrence of sep, and return a 3-tuple containing the part before the separator, the separator itself, and the part after the separator. If the separator is not found, return a 3-tuple containing the string itself, followed by two empty strings.

  sep must not be empty.

  On error, return `NULL` with an exception set.

  Equivalent to `str.partition()`.

PyObject *PyUnicode_RPartition(PyObject *unicode, PyObject *sep)
  Return value: New reference. Part of the Stable ABI.

  Similar to `PyUnicode_Partition()`, but split a Unicode string at the last occurrence of sep. If the separator is not found, return a 3-tuple containing two empty strings, followed by the string itself.

  sep must not be empty.

  On error, return `NULL` with an exception set.

  Equivalent to `str.rpartition()`.

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.

  See also

  The `PyUnicode_Equal()` function.

int PyUnicode_Equal(PyObject *a, PyObject *b)
  Part of the Stable ABI since version 3.14.

  Test if two strings are equal:

  - Return `1` if a is equal to b.

  - Return `0` if a is not equal to b.

  - Set a `TypeError` exception and return `-1` if a or b is not a `str` object.

  The function always succeeds if a and b are `str` objects.

  The function works for `str` subclasses, but does not honor custom `__eq__()` method.

  See also

  The `PyUnicode_Compare()` function.

  Added in version 3.14.

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.

unsigned int PyUnicode_CHECK_INTERNED(PyObject *str)

  Return a non-zero value if str is interned, zero if not. The str argument must be a string; this is not checked. This function always succeeds.

  CPython implementation detail: A non-zero return value may carry additional information about how the string is interned. The meaning of such non-zero values, as well as each specific string’s intern-related details, may change between CPython versions.

## PyUnicodeWriter

The `PyUnicodeWriter` API can be used to create a Python `str` object.

Added in version 3.14.

type PyUnicodeWriter

  A Unicode writer instance.

  The instance must be destroyed by `PyUnicodeWriter_Finish()` on success, or `PyUnicodeWriter_Discard()` on error.

PyUnicodeWriter *PyUnicodeWriter_Create(Py_ssize_t length)

  Create a Unicode writer instance.

  length must be greater than or equal to `0`.

  If length is greater than `0`, preallocate an internal buffer of length characters.

  Set an exception and return `NULL` on error.

PyObject *PyUnicodeWriter_Finish(PyUnicodeWriter *writer)

  Return the final Python `str` object and destroy the writer instance.

  Set an exception and return `NULL` on error.

  The writer instance is invalid after this call.

void PyUnicodeWriter_Discard(PyUnicodeWriter *writer)

  Discard the internal Unicode buffer and destroy the writer instance.

  If writer is `NULL`, no operation is performed.

  The writer instance is invalid after this call.

int PyUnicodeWriter_WriteChar(PyUnicodeWriter *writer, Py_UCS4 ch)

  Write the single Unicode character ch into writer.

  On success, return `0`. On error, set an exception, leave the writer unchanged, and return `-1`.

int PyUnicodeWriter_WriteUTF8(PyUnicodeWriter *writer, const char *str, Py_ssize_t size)

  Decode the string str from UTF-8 in strict mode and write the output into writer.

  size is the string length in bytes. If size is equal to `-1`, call `strlen(str)` to get the string length.

  On success, return `0`. On error, set an exception, leave the writer unchanged, and return `-1`.

  See also `PyUnicodeWriter_DecodeUTF8Stateful()`.

int PyUnicodeWriter_WriteASCII(PyUnicodeWriter *writer, const char *str, Py_ssize_t size)

  Write the ASCII string str into writer.

  size is the string length in bytes. If size is equal to `-1`, call `strlen(str)` to get the string length.

  str must only contain ASCII characters. The behavior is undefined if str contains non-ASCII characters.

  On success, return `0`. On error, set an exception, leave the writer unchanged, and return `-1`.

  Added in version 3.14.

int PyUnicodeWriter_WriteWideChar(PyUnicodeWriter *writer, const wchar_t *str, Py_ssize_t size)

  Write the wide string str into writer.

  size is a number of wide characters. If size is equal to `-1`, call `wcslen(str)` to get the string length.

  On success, return `0`. On error, set an exception, leave the writer unchanged, and return `-1`.

int PyUnicodeWriter_WriteUCS4(PyUnicodeWriter *writer, Py_UCS4 *str, Py_ssize_t size)

  Writer the UCS4 string str into writer.

  size is a number of UCS4 characters.

  On success, return `0`. On error, set an exception, leave the writer unchanged, and return `-1`.

int PyUnicodeWriter_WriteStr(PyUnicodeWriter *writer, PyObject *obj)

  Call `PyObject_Str()` on obj and write the output into writer.

  On success, return `0`. On error, set an exception, leave the writer unchanged, and return `-1`.

int PyUnicodeWriter_WriteRepr(PyUnicodeWriter *writer, PyObject *obj)

  Call `PyObject_Repr()` on obj and write the output into writer.

  On success, return `0`. On error, set an exception, leave the writer unchanged, and return `-1`.

int PyUnicodeWriter_WriteSubstring(PyUnicodeWriter *writer, PyObject *str, Py_ssize_t start, Py_ssize_t end)

  Write the substring `str[start:end]` into writer.

  str must be Python `str` object. start must be greater than or equal to 0, and less than or equal to end. end must be less than or equal to str length.

  On success, return `0`. On error, set an exception, leave the writer unchanged, and return `-1`.

int PyUnicodeWriter_Format(PyUnicodeWriter *writer, const char *format, ...)

  Similar to `PyUnicode_FromFormat()`, but write the output directly into writer.

  On success, return `0`. On error, set an exception, leave the writer unchanged, and return `-1`.

int PyUnicodeWriter_DecodeUTF8Stateful(PyUnicodeWriter *writer, const char *string, Py_ssize_t length, const char *errors, Py_ssize_t *consumed)

  Decode the string str from UTF-8 with errors error handler and write the output into writer.

  size is the string length in bytes. If size is equal to `-1`, call `strlen(str)` to get the string length.

  errors is an error handler name, such as `"replace"`. If errors is `NULL`, use the strict error handler.

  If consumed is not `NULL`, set *consumed to the number of decoded bytes on success. If consumed is `NULL`, treat trailing incomplete UTF-8 byte sequences as an error.

  On success, return `0`. On error, set an exception, leave the writer unchanged, and return `-1`.

  See also `PyUnicodeWriter_WriteUTF8()`.

## Deprecated API

The following API is deprecated.

type Py_UNICODE

  This is a typedef of `wchar_t`, which is a 16-bit type or 32-bit type depending on the platform. Please use `wchar_t` directly instead.

  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.

int PyUnicode_READY(PyObject *unicode)

  Do nothing and return `0`. This API is kept only for backward compatibility, but there are no plans to remove it.

  Added in version 3.3.

  Deprecated since version 3.10: This API does nothing since Python 3.12. Previously, this needed to be called for each string created using the old API (`PyUnicode_FromUnicode()` or similar).

unsigned int PyUnicode_IS_READY(PyObject *unicode)

  Do nothing and return `1`. This API is kept only for backward compatibility, but there are no plans to remove it.

  Added in version 3.3.

  Deprecated since version 3.14: This API does nothing since Python 3.12. Previously, this could be called to check if `PyUnicode_READY()` is necessary.