These functions are useful when creating your own extensions functions and methods. Additional information and examples are available in Extending and Embedding the Python Interpreter.
The first three of these functions described, :cfunc:`PyArg_ParseTuple`, :cfunc:`PyArg_ParseTupleAndKeywords`, and :cfunc:`PyArg_Parse`, 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.
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.
This variant on s stores into two C variables, the first one a pointer to a character string, the second one its length. In this case the Python string may contain embedded null bytes. Unicode objects pass back a pointer to the default encoded string version of the object if such a conversion is possible. All other read-buffer compatible objects pass back a reference to the raw internal data representation.
Starting with Python 2.5 the type of the length argument can be controlled by defining the macro :cmacro:`PY_SSIZE_T_CLEAN` before including Python.h. If the macro is defined, length is a :ctype:`Py_ssize_t` rather than an int.
Similar to s#, this code fills a Py_buffer structure provided by the caller. The buffer gets locked, so that the caller can subsequently use the buffer even inside a Py_BEGIN_ALLOW_THREADS block; the caller is responsible for calling PyBuffer_Release with the structure after it has processed the data.
New in version 2.6.
This is to s* as z is to s.
New in version 2.6.
This variant on s is used for encoding Unicode and objects convertible to 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 :ctype:`const char\*` which points to the name of an encoding as a NUL-terminated string, or NULL, in which case the default encoding is used. An exception is raised if the named encoding is not known to Python. The second argument must be a :ctype:`char\*\*`; 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.
:cfunc:`PyArg_ParseTuple` 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 :cfunc:`PyMem_Free` to free the allocated buffer after use.
This variant on s# is used for encoding Unicode and objects convertible to 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 :ctype:`const char\*` which points to the name of an encoding as a NUL-terminated string, or NULL, in which case the default encoding is used. An exception is raised if the named encoding is not known to Python. The second argument must be a :ctype:`char\*\*`; 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 :cfunc:`PyMem_Free` to free the allocated buffer after usage.
If *buffer points to a non-NULL pointer (an already allocated buffer), :cfunc:`PyArg_ParseTuple` 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 will be set.
In both cases, *buffer_length is set to the length of the encoded data without the trailing NUL byte.
Convert a Python integer to a tiny int without overflow checking, stored in a C :ctype:`unsigned char`.
New in version 2.3.
Convert a Python integer to a C :ctype:`unsigned short int`, without overflow checking.
New in version 2.3.
Convert a Python integer to a C :ctype:`unsigned int`, without overflow checking.
New in version 2.3.
Convert a Python integer or long integer to a C :ctype:`unsigned long` without overflow checking.
New in version 2.3.
Convert a Python integer or long integer to a C :ctype:`unsigned long long` without overflow checking. This format is only available on platforms that support :ctype:`unsigned long long` (or :ctype:`unsigned _int64` on Windows).
New in version 2.3.
Convert a Python integer or long integer to a C :ctype:`Py_ssize_t`.
New in version 2.5.
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 :ctype:`void \*`. The converter function in turn is called as follows:
status = converter(object, address);
where object is the Python object to be converted and address is the :ctype:`void\*` argument that was passed to the :cfunc:`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.
This is to w what s* is to s.
New in version 2.6.
The object must be a Python sequence 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.
Note
Prior to Python version 1.5.2, this format specifier only accepted a tuple containing the individual parameters, not an arbitrary sequence. Code which previously caused TypeError to be raised here may now proceed without an exception. This is not expected to be a problem for existing code.
It is possible to pass Python long integers where integers are requested; however no proper range checking is done — the most significant bits are silently truncated when the receiving field is too small to receive the value (actually, the semantics are inherited from downcasts in C — your mileage may vary).
A few other characters have a meaning in a format string. These may not occur inside nested parentheses. They are:
Note that any Python object references which are provided to the caller are borrowed references; 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 :cfunc:`PyArg_Parse\*` functions return true, otherwise they return false and raise an appropriate exception. When the :cfunc:`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.