Unicode Objects and Codecs

Unicode Objects

Since the implementation of 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 623 for more information.

Unicode Type

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

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

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

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

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

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

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

3.3

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).

3.3

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

3.3

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

Accept reading the trailing null character at index PyUnicode_GetLength.

3.3

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.

Accept reading the trailing null character at index PyUnicode_GetLength.

3.3

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.

3.3

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

3.9 The function does not call Py_FatalError anymore if the string is not ready.

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

3.2

If the hash of str, as returned by PyObject_Hash, has been cached and is immediately available, return it. Otherwise, return -1 without setting an exception.

If str is not a string (that is, if PyUnicode_Check(obj) is false), the behavior is undefined.

This function never fails with an exception.

Note that there are no guarantees on when an object's hash is cached, and the (non-)existence of a cached hash does not imply that the string has any other properties.

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.

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

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

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

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

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

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

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

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

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

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

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:

Return the character ch converted to lower case.

Return the character ch converted to upper case.

Return the character ch converted to title case.

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

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

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:

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

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

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

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

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

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:

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

3.12 str == NULL with size > 0 is not allowed anymore.

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

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:

|l|L|

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):

|l|L|

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).

3.2 Support for "%lld" and "%llu" added.

3.3 Support for "%li", "%lli" and "%zi" added.

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

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.

3.13 Support for %T, %#T, %N and %#N formats added.

Identical to PyUnicode_FromFormat except that it takes exactly two arguments.

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.

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.

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 <steal>") 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.

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

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.

3.2

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.

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

On error, set an exception and return -1.

The length does not count the trailing null character.

3.3

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.

Do not accept reading the trailing null character at index PyUnicode_GetLength.

3.3

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.

3.3

Locale Encoding

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

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

3.3

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" (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 <utf8-mode>.

The Py_EncodeLocale function.

3.3

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 (383 and 529).

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

PyArg_Parse\* converter <arg-parsing>: 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 <bytesobjects> 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.

3.1

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:

PyArg_Parse\* converter <arg-parsing>: 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 <unicodeobjects> 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.

3.2

3.6 Accepts a path-like object.

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.

The Py_DecodeLocale function.

3.6 The filesystem error handler <filesystem encoding and error handler> is now used.

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

If the string length is known, use PyUnicode_DecodeFSDefaultAndSize.

3.6 The filesystem error handler <filesystem encoding and error handler> is now used.

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.

The Py_EncodeLocale function.

3.2

3.6 The filesystem error handler <filesystem encoding and error handler> is now used.

wchar_t Support

wchar_t support for platforms which support it:

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.

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.

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.

3.2

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:

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:

UTF-8 Codecs

These are the UTF-8 codec APIs:

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.

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).

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.

3.3

3.7 The return type is now const char * rather than char *.

3.10 This function is a part of the limited API <limited-c-api>.

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.

3.3

3.7 The return type is now const char * rather than char *.

UTF-32 Codecs

These are the UTF-32 codec APIs:

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:

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:

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.

Unicode-Escape Codecs

These are the "Unicode Escape" codec APIs:

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:

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.

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.

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.

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

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 ~object.__getitem__ mapping interface; dictionaries and sequences work well.

These are the mapping codec APIs:

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.

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 ~object.__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.

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

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.

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.

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.

Concat two strings giving a new Unicode string.

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.

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.

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.

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.

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.

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

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.

The PyUnicode_Equal function.

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.

The PyUnicode_Compare function.

3.14

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.

3.13

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

3.13

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.

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.

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

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.

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.

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.

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.

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.

A Unicode writer instance.

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

The API is not thread safe. To share a writer with multiple threads, a critical section or a lock is needed.

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.

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.

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.

Write the single Unicode character ch into writer.

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

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.

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.

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.

Write the UCS4 string str into writer.

size is a number of UCS4 characters.

All characters must be in range [U+0000; U+10ffff]. If the string contains invalid characters, the behavior is undefined.

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

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.

To write a str subclass which overrides the ~object.__str__ method, PyUnicode_FromObject can be used to get the original string.

Call PyObject_Repr on obj and write the output into writer.

If obj is NULL, write the string "<NULL>" into writer.

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

3.14.4

Added support for NULL.

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.

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.

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 <error-handlers> 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.

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.

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.

3.13 3.16

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

3.3

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).

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

3.3

3.14 This API does nothing since Python 3.12. Previously, this could be called to check if PyUnicode_READY is necessary.

Mutating string objects

The following functions allow creating a blank string object of a given size, then filling in its contents. They are soft deprecated: they break the assumption that strings are immutable, making them hard to use correctly.

Prefer using the PyUnicodeWriter API, or one of the PyUnicode_From* functions such as PyUnicode_FromStringAndSize.

If you do use the functions below, take care to not "use" such a string 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 <PyUnicode_AsUTF8AndSize>, or another non-"canonical" representation,
• must not have its reference count changed,
• must not be accessed from another thread,
• 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.

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.

See pyunicode-new-mutating for important warnings and caveats.

3.3

3.16 See pyunicode-new-mutating.

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.

*unicode must not be "used" yet. See pyunicode-new-mutating for details.

3.16 Use the PyUnicodeWriter API instead.