python_doc_md/Advanced/c-api/arg.md

Parsing arguments and building values {#arg-parsing}

These functions are useful when creating your own extension functions and methods. Additional information and examples are available in extending-index{.interpreted-text role="ref"}.

The first three of these functions described, PyArg_ParseTuple{.interpreted-text role="c:func"}, PyArg_ParseTupleAndKeywords{.interpreted-text role="c:func"}, and PyArg_Parse{.interpreted-text role="c:func"}, all use format strings which are used to tell the function about the expected arguments. The format strings use the same syntax for each of these functions.

Parsing arguments

A format string consists of zero or more "format units." A format unit describes one Python object; it is usually a single character or a parenthesized sequence of format units. With a few exceptions, a format unit that is not a parenthesized sequence normally corresponds to a single address argument to these functions. In the following description, the quoted form is the format unit; the entry in (round) parentheses is the Python object type that matches the format unit; and the entry in [square] brackets is the type of the C variable(s) whose address should be passed.

Strings and buffers {#arg-parsing-string-and-buffers}

:::: note ::: title Note :::

On Python 3.12 and older, the macro !PY_SSIZE_T_CLEAN{.interpreted-text role="c:macro"} must be defined before including Python.h{.interpreted-text role="file"} to use all # variants of formats (s#, y#, etc.) explained below. This is not necessary on Python 3.13 and later. ::::

These formats allow accessing an object as a contiguous chunk of memory. You don't have to provide raw storage for the returned unicode or bytes area.

Unless otherwise stated, buffers are not NUL-terminated.

There are three ways strings and buffers can be converted to C:

• Formats such as y* and s* fill a Py_buffer{.interpreted-text role="c:type"} structure. This locks the underlying buffer so that the caller can subsequently use the buffer even inside a Py_BEGIN_ALLOW_THREADS{.interpreted-text role="c:type"} block without the risk of mutable data being resized or destroyed. As a result, you have to call PyBuffer_Release{.interpreted-text role="c:func"} after you have finished processing the data (or in any early abort case).

• The es, es#, et and et# formats allocate the result buffer. You have to call PyMem_Free{.interpreted-text role="c:func"} after you have finished processing the data (or in any early abort case).

• ::: {#c-arg-borrowed-buffer} Other formats take a str{.interpreted-text role="class"} or a read-only bytes-like object{.interpreted-text role="term"}, such as bytes{.interpreted-text role="class"}, and provide a const char * pointer to its buffer. In this case the buffer is "borrowed": it is managed by the corresponding Python object, and shares the lifetime of this object. You won't have to release any memory yourself. :::

  To ensure that the underlying buffer may be safely borrowed, the object's PyBufferProcs.bf_releasebuffer{.interpreted-text role="c:member"} field must be NULL. This disallows common mutable objects such as bytearray{.interpreted-text role="class"}, but also some read-only objects such as memoryview{.interpreted-text role="class"} of bytes{.interpreted-text role="class"}.

  Besides this bf_releasebuffer requirement, there is no check to verify whether the input object is immutable (e.g. whether it would honor a request for a writable buffer, or whether another thread can mutate the data).

s (str{.interpreted-text role="class"}) [const char *]

: Convert a Unicode object to a C pointer to a character string. A pointer to an existing string is stored in the character pointer variable whose address you pass. The C string is NUL-terminated. The Python string must not contain embedded null code points; if it does, a ValueError{.interpreted-text role="exc"} exception is raised. Unicode objects are converted to C strings using 'utf-8' encoding. If this conversion fails, a UnicodeError{.interpreted-text role="exc"} is raised.

:::: note
::: title
Note
:::

This format does not accept `bytes-like objects
<bytes-like object>`{.interpreted-text role="term"}. If you want to accept filesystem paths and convert them to C character strings, it is preferable to use the `O&` format with `PyUnicode_FSConverter`{.interpreted-text role="c:func"} as *converter*.
::::

::: versionchanged
3.5 Previously, `TypeError`{.interpreted-text role="exc"} was raised when embedded null code points were encountered in the Python string.
:::

s* (str{.interpreted-text role="class"} or bytes-like object{.interpreted-text role="term"}) [Py_buffer]

: This format accepts Unicode objects as well as bytes-like objects. It fills a Py_buffer{.interpreted-text role="c:type"} structure provided by the caller. In this case the resulting C string may contain embedded NUL bytes. Unicode objects are converted to C strings using 'utf-8' encoding.

s# (str{.interpreted-text role="class"}, read-only bytes-like object{.interpreted-text role="term"}) [const char *, Py_ssize_t{.interpreted-text role="c:type"}]

: Like s*, except that it provides a borrowed buffer <c-arg-borrowed-buffer>{.interpreted-text role="ref"}. The result is stored into two C variables, the first one a pointer to a C string, the second one its length. The string may contain embedded null bytes. Unicode objects are converted to C strings using 'utf-8' encoding.

z (str{.interpreted-text role="class"} or None) [const char *]

: Like s, but the Python object may also be None, in which case the C pointer is set to NULL.

z* (str{.interpreted-text role="class"}, bytes-like object{.interpreted-text role="term"} or None) [Py_buffer]

: Like s*, but the Python object may also be None, in which case the buf member of the Py_buffer{.interpreted-text role="c:type"} structure is set to NULL.

z# (str{.interpreted-text role="class"}, read-only bytes-like object{.interpreted-text role="term"} or None) [const char *, Py_ssize_t{.interpreted-text role="c:type"}]

: Like s#, but the Python object may also be None, in which case the C pointer is set to NULL.

y (read-only bytes-like object{.interpreted-text role="term"}) [const char *]

: This format converts a bytes-like object to a C pointer to a borrowed <c-arg-borrowed-buffer>{.interpreted-text role="ref"} character string; it does not accept Unicode objects. The bytes buffer must not contain embedded null bytes; if it does, a ValueError{.interpreted-text role="exc"} exception is raised.

::: versionchanged
3.5 Previously, `TypeError`{.interpreted-text role="exc"} was raised when embedded null bytes were encountered in the bytes buffer.
:::

y* (bytes-like object{.interpreted-text role="term"}) [Py_buffer]

: This variant on s* doesn't accept Unicode objects, only bytes-like objects. This is the recommended way to accept binary data.

y# (read-only bytes-like object{.interpreted-text role="term"}) [const char *, Py_ssize_t{.interpreted-text role="c:type"}]

: This variant on s# doesn't accept Unicode objects, only bytes-like objects.

S (bytes{.interpreted-text role="class"}) [PyBytesObject *]

: Requires that the Python object is a bytes{.interpreted-text role="class"} object, without attempting any conversion. Raises TypeError{.interpreted-text role="exc"} if the object is not a bytes object. The C variable may also be declared as PyObject*{.interpreted-text role="c:expr"}.

Y (bytearray{.interpreted-text role="class"}) [PyByteArrayObject *]

: Requires that the Python object is a bytearray{.interpreted-text role="class"} object, without attempting any conversion. Raises TypeError{.interpreted-text role="exc"} if the object is not a bytearray{.interpreted-text role="class"} object. The C variable may also be declared as PyObject*{.interpreted-text role="c:expr"}.

U (str{.interpreted-text role="class"}) [PyObject *]

: Requires that the Python object is a Unicode object, without attempting any conversion. Raises TypeError{.interpreted-text role="exc"} if the object is not a Unicode object. The C variable may also be declared as PyObject*{.interpreted-text role="c:expr"}.

w* (read-write bytes-like object{.interpreted-text role="term"}) [Py_buffer]

: This format accepts any object which implements the read-write buffer interface. It fills a Py_buffer{.interpreted-text role="c:type"} structure provided by the caller. The buffer may contain embedded null bytes. The caller has to call PyBuffer_Release{.interpreted-text role="c:func"} when it is done with the buffer.

es (str{.interpreted-text role="class"}) [const char *encoding, char **buffer]

: This variant on s is used for encoding Unicode into a character buffer. It only works for encoded data without embedded NUL bytes.

This format requires two arguments. The first is only used as input, and must be a `const char*`{.interpreted-text role="c:expr"} which points to the name of an encoding as a NUL-terminated string, or `NULL`, in which case `'utf-8'` encoding is used. An exception is raised if the named encoding is not known to Python. The second argument must be a `char**`{.interpreted-text role="c:expr"}; the value of the pointer it references will be set to a buffer with the contents of the argument text. The text will be encoded in the encoding specified by the first argument.

`PyArg_ParseTuple`{.interpreted-text role="c:func"} will allocate a buffer of the needed size, copy the encoded data into this buffer and adjust *\*buffer* to reference the newly allocated storage. The caller is responsible for calling `PyMem_Free`{.interpreted-text role="c:func"} to free the allocated buffer after use.

et (str{.interpreted-text role="class"}, bytes{.interpreted-text role="class"} or bytearray{.interpreted-text role="class"}) [const char *encoding, char **buffer]

: Same as es except that byte string objects are passed through without recoding them. Instead, the implementation assumes that the byte string object uses the encoding passed in as parameter.

es# (str{.interpreted-text role="class"}) [const char *encoding, char **buffer, Py_ssize_t{.interpreted-text role="c:type"} *buffer_length]

: This variant on s# is used for encoding Unicode into a character buffer. Unlike the es format, this variant allows input data which contains NUL characters.

It requires three arguments. The first is only used as input, and must be a `const char*`{.interpreted-text role="c:expr"} which points to the name of an encoding as a NUL-terminated string, or `NULL`, in which case `'utf-8'` encoding is used. An exception is raised if the named encoding is not known to Python. The second argument must be a `char**`{.interpreted-text role="c:expr"}; the value of the pointer it references will be set to a buffer with the contents of the argument text. The text will be encoded in the encoding specified by the first argument. The third argument must be a pointer to an integer; the referenced integer will be set to the number of bytes in the output buffer.

There are two modes of operation:

If *\*buffer* points a `NULL` pointer, the function will allocate a buffer of the needed size, copy the encoded data into this buffer and set *\*buffer* to reference the newly allocated storage. The caller is responsible for calling `PyMem_Free`{.interpreted-text role="c:func"} to free the allocated buffer after usage.

If *\*buffer* points to a non-`NULL` pointer (an already allocated buffer), `PyArg_ParseTuple`{.interpreted-text role="c:func"} will use this location as the buffer and interpret the initial value of *\*buffer_length* as the buffer size. It will then copy the encoded data into the buffer and NUL-terminate it. If the buffer is not large enough, a `ValueError`{.interpreted-text role="exc"} will be set.

In both cases, *\*buffer_length* is set to the length of the encoded data without the trailing NUL byte.

et# (str{.interpreted-text role="class"}, bytes{.interpreted-text role="class"} or bytearray{.interpreted-text role="class"}) [const char *encoding, char **buffer, Py_ssize_t{.interpreted-text role="c:type"} *buffer_length]

: Same as es# except that byte string objects are passed through without recoding them. Instead, the implementation assumes that the byte string object uses the encoding passed in as parameter.

::: versionchanged 3.12 u, u#, Z, and Z# are removed because they used a legacy Py_UNICODE* representation. :::

Numbers

These formats allow representing Python numbers or single characters as C numbers. Formats that require int{.interpreted-text role="class"}, float{.interpreted-text role="class"} or complex{.interpreted-text role="class"} can also use the corresponding special methods ~object.__index__{.interpreted-text role="meth"}, ~object.__float__{.interpreted-text role="meth"} or ~object.__complex__{.interpreted-text role="meth"} to convert the Python object to the required type.

For signed integer formats, OverflowError{.interpreted-text role="exc"} is raised if the value is out of range for the C type. For unsigned integer formats, the most significant bits are silently truncated when the receiving field is too small to receive the value, and DeprecationWarning{.interpreted-text role="exc"} is emitted when the value is larger than the maximal value for the C type or less than the minimal value for the corresponding signed integer type of the same size.

b (int{.interpreted-text role="class"}) [unsigned char]

: Convert a nonnegative Python integer to an unsigned tiny integer, stored in a C unsigned char{.interpreted-text role="c:expr"}.

B (int{.interpreted-text role="class"}) [unsigned char]

: Convert a Python integer to a tiny integer without overflow checking, stored in a C unsigned char{.interpreted-text role="c:expr"}. Convert a Python integer to a C unsigned char{.interpreted-text role="c:expr"}.

h (int{.interpreted-text role="class"}) [short int]

: Convert a Python integer to a C short int{.interpreted-text role="c:expr"}.

H (int{.interpreted-text role="class"}) [unsigned short int]

: Convert a Python integer to a C unsigned short int{.interpreted-text role="c:expr"}.

i (int{.interpreted-text role="class"}) [int]

: Convert a Python integer to a plain C int{.interpreted-text role="c:expr"}.

I (int{.interpreted-text role="class"}) [unsigned int]

: Convert a Python integer to a C unsigned int{.interpreted-text role="c:expr"}.

l (int{.interpreted-text role="class"}) [long int]

: Convert a Python integer to a C long int{.interpreted-text role="c:expr"}.

k (int{.interpreted-text role="class"}) [unsigned long]

: Convert a Python integer to a C unsigned long{.interpreted-text role="c:expr"}.

::: versionchanged
3.14 Use `~object.__index__`{.interpreted-text role="meth"} if available.
:::

L (int{.interpreted-text role="class"}) [long long]

: Convert a Python integer to a C long long{.interpreted-text role="c:expr"}.

K (int{.interpreted-text role="class"}) [unsigned long long]

: Convert a Python integer to a C unsigned long long{.interpreted-text role="c:expr"}.

::: versionchanged
3.14 Use `~object.__index__`{.interpreted-text role="meth"} if available.
:::

n (int{.interpreted-text role="class"}) [Py_ssize_t{.interpreted-text role="c:type"}]

: Convert a Python integer to a C Py_ssize_t{.interpreted-text role="c:type"}.

c (bytes{.interpreted-text role="class"} or bytearray{.interpreted-text role="class"} of length 1) [char]

: Convert a Python byte, represented as a bytes{.interpreted-text role="class"} or bytearray{.interpreted-text role="class"} object of length 1, to a C char{.interpreted-text role="c:expr"}.

::: versionchanged
3.3 Allow `bytearray`{.interpreted-text role="class"} objects.
:::

C (str{.interpreted-text role="class"} of length 1) [int]

: Convert a Python character, represented as a str{.interpreted-text role="class"} object of length 1, to a C int{.interpreted-text role="c:expr"}.

f (float{.interpreted-text role="class"}) [float]

: Convert a Python floating-point number to a C float{.interpreted-text role="c:expr"}.

d (float{.interpreted-text role="class"}) [double]

: Convert a Python floating-point number to a C double{.interpreted-text role="c:expr"}.

D (complex{.interpreted-text role="class"}) [Py_complex]

: Convert a Python complex number to a C Py_complex{.interpreted-text role="c:type"} structure.

::: deprecated 3.15

For unsigned integer formats B, H, I, k and K, DeprecationWarning{.interpreted-text role="exc"} is emitted when the value is larger than the maximal value for the C type or less than the minimal value for the corresponding signed integer type of the same size. :::

Other objects

O (object) [PyObject *]

: Store a Python object (without any conversion) in a C object pointer. The C program thus receives the actual object that was passed. A new strong reference{.interpreted-text role="term"} to the object is not created (i.e. its reference count is not increased). The pointer stored is not NULL.

O! (object) [typeobject, PyObject *]

: Store a Python object in a C object pointer. This is similar to O, but takes two C arguments: the first is the address of a Python type object, the second is the address of the C variable (of type PyObject*{.interpreted-text role="c:expr"}) into which the object pointer is stored. If the Python object does not have the required type, TypeError{.interpreted-text role="exc"} is raised.

::: {#o_ampersand}

O& (object) [converter, address]

: Convert a Python object to a C variable through a converter function. This takes two arguments: the first is a function, the second is the address of a C variable (of arbitrary type), converted to void *{.interpreted-text role="c:expr"}. The converter function in turn is called as follows:

``` c
status = converter(object, address);
```

where *object* is the Python object to be converted and *address* is the `void*`{.interpreted-text role="c:expr"} argument that was passed to the `PyArg_Parse*` function. The returned *status* should be `1` for a successful conversion and `0` if the conversion has failed. When the conversion fails, the *converter* function should raise an exception and leave the content of *address* unmodified.

If the *converter* returns `!Py_CLEANUP_SUPPORTED`{.interpreted-text role="c:macro"}, it may get called a second time if the argument parsing eventually fails, giving the converter a chance to release any memory that it had already allocated. In this second call, the *object* parameter will be `NULL`; *address* will have the same value as in the original call.

Examples of converters: `PyUnicode_FSConverter`{.interpreted-text role="c:func"} and `PyUnicode_FSDecoder`{.interpreted-text role="c:func"}.

::: versionchanged
3.1 `!Py_CLEANUP_SUPPORTED`{.interpreted-text role="c:macro"} was added.
:::

p (bool{.interpreted-text role="class"}) [int]

: Tests the value passed in for truth (a boolean predicate) and converts the result to its equivalent C true/false integer value. Sets the int to 1 if the expression was true and 0 if it was false. This accepts any valid Python value. See truth{.interpreted-text role="ref"} for more information about how Python tests values for truth.

::: versionadded
3.3
:::

(items) (sequence) [matching-items]

: The object must be a Python sequence (except str{.interpreted-text role="class"}, bytes{.interpreted-text role="class"} or bytearray{.interpreted-text role="class"}) whose length is the number of format units in items. The C arguments must correspond to the individual format units in items. Format units for sequences may be nested.

If *items* contains format units which store a `borrowed buffer
<c-arg-borrowed-buffer>`{.interpreted-text role="ref"} (`s`, `s#`, `z`, `z#`, `y`, or `y#`) or a `borrowed reference`{.interpreted-text role="term"} (`S`, `Y`, `U`, `O`, or `O!`), the object must be a Python tuple. The *converter* for the `O&` format unit in *items* must not store a borrowed buffer or a borrowed reference.

::: versionchanged
3.14 `str`{.interpreted-text role="class"} and `bytearray`{.interpreted-text role="class"} objects no longer accepted as a sequence.
:::

::: deprecated
3.14 Non-tuple sequences are deprecated if *items* contains format units which store a borrowed buffer or a borrowed reference.
:::

:::

A few other characters have a meaning in a format string. These may not occur inside nested parentheses. They are:

|

: Indicates that the remaining arguments in the Python argument list are optional. The C variables corresponding to optional arguments should be initialized to their default value --- when an optional argument is not specified, PyArg_ParseTuple{.interpreted-text role="c:func"} does not touch the contents of the corresponding C variable(s).

$

: PyArg_ParseTupleAndKeywords{.interpreted-text role="c:func"} only: Indicates that the remaining arguments in the Python argument list are keyword-only. Currently, all keyword-only arguments must also be optional arguments, so | must always be specified before $ in the format string.

::: versionadded
3.3
:::

:

: The list of format units ends here; the string after the colon is used as the function name in error messages (the "associated value" of the exception that PyArg_ParseTuple{.interpreted-text role="c:func"} raises).

;

: The list of format units ends here; the string after the semicolon is used as the error message instead of the default error message. : and ; mutually exclude each other.

Note that any Python object references which are provided to the caller are borrowed references; do not release them (i.e. do not decrement their reference count)!

Additional arguments passed to these functions must be addresses of variables whose type is determined by the format string; these are used to store values from the input tuple. There are a few cases, as described in the list of format units above, where these parameters are used as input values; they should match what is specified for the corresponding format unit in that case.

For the conversion to succeed, the arg object must match the format and the format must be exhausted. On success, the PyArg_Parse* functions return true, otherwise they return false and raise an appropriate exception. When the PyArg_Parse* functions fail due to conversion failure in one of the format units, the variables at the addresses corresponding to that and the following format units are left untouched.

API Functions

Parse the parameters of a function that takes only positional parameters into local variables. Returns true on success; on failure, it returns false and raises the appropriate exception.

Identical to PyArg_ParseTuple{.interpreted-text role="c:func"}, except that it accepts a va_list rather than a variable number of arguments.

Parse the parameters of a function that takes both positional and keyword parameters into local variables. The keywords argument is a NULL-terminated array of keyword parameter names specified as null-terminated ASCII or UTF-8 encoded C strings. Empty names denote positional-only parameters <positional-only_parameter>{.interpreted-text role="ref"}. Returns true on success; on failure, it returns false and raises the appropriate exception.

:::: note ::: title Note :::

The keywords parameter declaration is char * const *{.interpreted-text role="c:expr"} in C and const char * const *{.interpreted-text role="c:expr"} in C++. This can be overridden with the PY_CXX_CONST{.interpreted-text role="c:macro"} macro. ::::

::: versionchanged 3.6 Added support for positional-only parameters <positional-only_parameter>{.interpreted-text role="ref"}. :::

::: versionchanged 3.13 The keywords parameter has now type char * const *{.interpreted-text role="c:expr"} in C and const char * const *{.interpreted-text role="c:expr"} in C++, instead of char **{.interpreted-text role="c:expr"}. Added support for non-ASCII keyword parameter names. :::

Identical to PyArg_ParseTupleAndKeywords{.interpreted-text role="c:func"}, except that it accepts a va_list rather than a variable number of arguments.

Ensure that the keys in the keywords argument dictionary are strings. This is only needed if PyArg_ParseTupleAndKeywords{.interpreted-text role="c:func"} is not used, since the latter already does this check.

::: versionadded 3.2 :::

Parse the parameter of a function that takes a single positional parameter into a local variable. Returns true on success; on failure, it returns false and raises the appropriate exception.

Example:

// Function using METH_O calling convention
static PyObject*
my_function(PyObject *module, PyObject *arg)
{
    int value;
    if (!PyArg_Parse(arg, "i:my_function", &value)) {
        return NULL;
    }
    // ... use value ...
}

A simpler form of parameter retrieval which does not use a format string to specify the types of the arguments. Functions which use this method to retrieve their parameters should be declared as METH_VARARGS{.interpreted-text role="c:macro"} in function or method tables. The tuple containing the actual parameters should be passed as args; it must actually be a tuple. The length of the tuple must be at least min and no more than max; min and max may be equal. Additional arguments must be passed to the function, each of which should be a pointer to a PyObject*{.interpreted-text role="c:expr"} variable; these will be filled in with the values from args; they will contain borrowed references <borrowed reference>{.interpreted-text role="term"}. The variables which correspond to optional parameters not given by args will not be filled in; these should be initialized by the caller. This function returns true on success and false if args is not a tuple or contains the wrong number of elements; an exception will be set if there was a failure.

This is an example of the use of this function, taken from the sources for the !_weakref{.interpreted-text role="mod"} helper module for weak references:

static PyObject *
weakref_ref(PyObject *self, PyObject *args)
{
    PyObject *object;
    PyObject *callback = NULL;
    PyObject *result = NULL;

    if (PyArg_UnpackTuple(args, "ref", 1, 2, &object, &callback)) {
        result = PyWeakref_NewRef(object, callback);
    }
    return result;
}

The call to PyArg_UnpackTuple{.interpreted-text role="c:func"} in this example is entirely equivalent to this call to PyArg_ParseTuple{.interpreted-text role="c:func"}:

PyArg_ParseTuple(args, "O|O:ref", &object, &callback)

The value to be inserted, if any, before char * const *{.interpreted-text role="c:expr"} in the keywords parameter declaration of PyArg_ParseTupleAndKeywords{.interpreted-text role="c:func"} and PyArg_VaParseTupleAndKeywords{.interpreted-text role="c:func"}. Default empty for C and const for C++ (const char * const *{.interpreted-text role="c:expr"}). To override, define it to the desired value before including Python.h{.interpreted-text role="file"}.

::: versionadded 3.13 :::

Building values

Create a new value based on a format string similar to those accepted by the PyArg_Parse* family of functions and a sequence of values. Returns the value or NULL in the case of an error; an exception will be raised if NULL is returned.

Py_BuildValue{.interpreted-text role="c:func"} does not always build a tuple. It builds a tuple only if its format string contains two or more format units. If the format string is empty, it returns None; if it contains exactly one format unit, it returns whatever object is described by that format unit. To force it to return a tuple of size 0 or one, parenthesize the format string.

When memory buffers are passed as parameters to supply data to build objects, as for the s and s# formats, the required data is copied. Buffers provided by the caller are never referenced by the objects created by Py_BuildValue{.interpreted-text role="c:func"}. In other words, if your code invokes malloc{.interpreted-text role="c:func"} and passes the allocated memory to Py_BuildValue{.interpreted-text role="c:func"}, your code is responsible for calling free{.interpreted-text role="c:func"} for that memory once Py_BuildValue{.interpreted-text role="c:func"} returns.

In the following description, the quoted form is the format unit; the entry in (round) parentheses is the Python object type that the format unit will return; and the entry in [square] brackets is the type of the C value(s) to be passed.

The characters space, tab, colon and comma are ignored in format strings (but not within format units such as s#). This can be used to make long format strings a tad more readable.

s (str{.interpreted-text role="class"} or None) [const char *]

: Convert a null-terminated C string to a Python str{.interpreted-text role="class"} object using 'utf-8' encoding. If the C string pointer is NULL, None is used.

s# (str{.interpreted-text role="class"} or None) [const char *, Py_ssize_t{.interpreted-text role="c:type"}]

: Convert a C string and its length to a Python str{.interpreted-text role="class"} object using 'utf-8' encoding. If the C string pointer is NULL, the length is ignored and None is returned.

y (bytes{.interpreted-text role="class"}) [const char *]

: This converts a C string to a Python bytes{.interpreted-text role="class"} object. If the C string pointer is NULL, None is returned.

y# (bytes{.interpreted-text role="class"}) [const char *, Py_ssize_t{.interpreted-text role="c:type"}]

: This converts a C string and its lengths to a Python object. If the C string pointer is NULL, None is returned.

z (str{.interpreted-text role="class"} or None) [const char *]

: Same as s.

z# (str{.interpreted-text role="class"} or None) [const char *, Py_ssize_t{.interpreted-text role="c:type"}]

: Same as s#.

u (str{.interpreted-text role="class"}) [const wchar_t *]

: Convert a null-terminated wchar_t{.interpreted-text role="c:type"} buffer of Unicode (UTF-16 or UCS-4) data to a Python Unicode object. If the Unicode buffer pointer is NULL, None is returned.

u# (str{.interpreted-text role="class"}) [const wchar_t *, Py_ssize_t{.interpreted-text role="c:type"}]

: Convert a Unicode (UTF-16 or UCS-4) data buffer and its length to a Python Unicode object. If the Unicode buffer pointer is NULL, the length is ignored and None is returned.

U (str{.interpreted-text role="class"} or None) [const char *]

: Same as s.

U# (str{.interpreted-text role="class"} or None) [const char *, Py_ssize_t{.interpreted-text role="c:type"}]

: Same as s#.

i (int{.interpreted-text role="class"}) [int]

: Convert a plain C int{.interpreted-text role="c:expr"} to a Python integer object.

b (int{.interpreted-text role="class"}) [char]

: Convert a plain C char{.interpreted-text role="c:expr"} to a Python integer object.

h (int{.interpreted-text role="class"}) [short int]

: Convert a plain C short int{.interpreted-text role="c:expr"} to a Python integer object.

l (int{.interpreted-text role="class"}) [long int]

: Convert a C long int{.interpreted-text role="c:expr"} to a Python integer object.

B (int{.interpreted-text role="class"}) [unsigned char]

: Convert a C unsigned char{.interpreted-text role="c:expr"} to a Python integer object.

H (int{.interpreted-text role="class"}) [unsigned short int]

: Convert a C unsigned short int{.interpreted-text role="c:expr"} to a Python integer object.

I (int{.interpreted-text role="class"}) [unsigned int]

: Convert a C unsigned int{.interpreted-text role="c:expr"} to a Python integer object.

k (int{.interpreted-text role="class"}) [unsigned long]

: Convert a C unsigned long{.interpreted-text role="c:expr"} to a Python integer object.

L (int{.interpreted-text role="class"}) [long long]

: Convert a C long long{.interpreted-text role="c:expr"} to a Python integer object.

::: {#capi-py-buildvalue-format-K}

K (int{.interpreted-text role="class"}) [unsigned long long]

: Convert a C unsigned long long{.interpreted-text role="c:expr"} to a Python integer object.

n (int{.interpreted-text role="class"}) [Py_ssize_t{.interpreted-text role="c:type"}]

: Convert a C Py_ssize_t{.interpreted-text role="c:type"} to a Python integer.

p (bool{.interpreted-text role="class"}) [int]

: Convert a C int{.interpreted-text role="c:expr"} to a Python bool{.interpreted-text role="class"} object.

Be aware that this format requires an `int` argument. Unlike most other contexts in C, variadic arguments are not coerced to a suitable type automatically. You can convert another type (for example, a pointer or a float) to a suitable `int` value using `(x) ? 1 : 0` or `!!x`.

::: versionadded
3.14
:::

c (bytes{.interpreted-text role="class"} of length 1) [char]

: Convert a C int{.interpreted-text role="c:expr"} representing a byte to a Python bytes{.interpreted-text role="class"} object of length 1.

C (str{.interpreted-text role="class"} of length 1) [int]

: Convert a C int{.interpreted-text role="c:expr"} representing a character to Python str{.interpreted-text role="class"} object of length 1.

d (float{.interpreted-text role="class"}) [double]

: Convert a C double{.interpreted-text role="c:expr"} to a Python floating-point number.

f (float{.interpreted-text role="class"}) [float]

: Convert a C float{.interpreted-text role="c:expr"} to a Python floating-point number.

D (complex{.interpreted-text role="class"}) [Py_complex *]

: Convert a C Py_complex{.interpreted-text role="c:type"} structure to a Python complex number.

O (object) [PyObject *]

: Pass a Python object untouched but create a new strong reference{.interpreted-text role="term"} to it (i.e. its reference count is incremented by one). If the object passed in is a NULL pointer, it is assumed that this was caused because the call producing the argument found an error and set an exception. Therefore, Py_BuildValue{.interpreted-text role="c:func"} will return NULL but won't raise an exception. If no exception has been raised yet, SystemError{.interpreted-text role="exc"} is set.

S (object) [PyObject *]

: Same as O.

N (object) [PyObject *]

: Same as O, except it doesn't create a new strong reference{.interpreted-text role="term"}. Useful when the object is created by a call to an object constructor in the argument list.

O& (object) [converter, anything]

: Convert anything to a Python object through a converter function. The function is called with anything (which should be compatible with void*{.interpreted-text role="c:expr"}) as its argument and should return a "new" Python object, or NULL if an error occurred.

(items) (tuple{.interpreted-text role="class"}) [matching-items]

: Convert a sequence of C values to a Python tuple with the same number of items.

[items] (list{.interpreted-text role="class"}) [matching-items]

: Convert a sequence of C values to a Python list with the same number of items.

{items} (dict{.interpreted-text role="class"}) [matching-items]

: Convert a sequence of C values to a Python dictionary. Each pair of consecutive C values adds one item to the dictionary, serving as key and value, respectively. :::

If there is an error in the format string, the SystemError{.interpreted-text role="exc"} exception is set and NULL returned.

Identical to Py_BuildValue{.interpreted-text role="c:func"}, except that it accepts a va_list rather than a variable number of arguments.