Parsing arguments and building values
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.
s (string or Unicode) [const char *]- Convert a Python string or Unicode object to a C pointer to a character
string. You must not provide storage for the string itself; a pointer to
an existing string is stored into the character pointer variable whose
address you pass. The C string is NUL-terminated. The Python string must
not contain embedded NUL bytes; if it does, a
TypeError exception is
raised. Unicode objects are converted to C strings using the default
encoding. If this conversion fails, a UnicodeError is raised.
s# (string, Unicode or any read buffer compatible object) [const char *, int (or :ctype:`Py_ssize_t`, see below)]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.
s* (string, Unicode, or any buffer compatible object) [Py_buffer]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:
New in version 2.6.
z (string, Unicode 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# (string, Unicode, None or any read buffer compatible object) [const char *, int]
This is to s# as z is to s.
z* (string, Unicode, None or any buffer compatible object) [Py_buffer]
This is to s* as z is to s.
New in version 2.6:
New in version 2.6.
u (Unicode) [Py_UNICODE *]
Convert a Python Unicode object to a C pointer to a NUL-terminated buffer
of 16-bit Unicode (UTF-16) data. As with s, there is no need to
provide storage for the Unicode data buffer; a pointer to the existing
Unicode data is stored into the :ctype:`Py_UNICODE` pointer variable whose
address you pass.
u# (Unicode) [Py_UNICODE *, int]
This variant on u stores into two C variables, the first one a pointer
to a Unicode data buffer, the second one its length. Non-Unicode objects
are handled by interpreting their read-buffer pointer as pointer to a
:ctype:`Py_UNICODE` array.
es (string, Unicode or character buffer compatible object) [const char *encoding, char **buffer]
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.
et (string, Unicode or character buffer compatible object) [const char *encoding, char **buffer]
Same as es except that 8-bit string objects are passed through without
recoding them. Instead, the implementation assumes that the string object
uses the encoding passed in as parameter.
es# (string, Unicode or character buffer compatible object) [const char *encoding, char **buffer, int *buffer_length]
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.
et# (string, Unicode or character buffer compatible object) [const char *encoding, char **buffer, int *buffer_length]
Same as es# except that string objects are passed through without
recoding them. Instead, the implementation assumes that the string object
uses the encoding passed in as parameter.
b (integer) [unsigned char]
Convert a nonnegative Python integer to an unsigned tiny int, stored in a C
:ctype:`unsigned char`.
B (integer) [unsigned char]
Convert a Python integer to a tiny int without overflow checking, stored in
a C :ctype:`unsigned char`.
New in version 2.3:
New in version 2.3.