677 lines
30 KiB
ReStructuredText
677 lines
30 KiB
ReStructuredText
.. highlight:: c
|
|
|
|
.. _arg-parsing:
|
|
|
|
Parsing arguments and building values
|
|
=====================================
|
|
|
|
These functions are useful when creating your own extensions functions and
|
|
methods. Additional information and examples are available in
|
|
:ref:`extending-index`.
|
|
|
|
The first three of these functions described, :c:func:`PyArg_ParseTuple`,
|
|
:c:func:`PyArg_ParseTupleAndKeywords`, and :c:func:`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.
|
|
|
|
-----------------
|
|
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
|
|
-------------------
|
|
|
|
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.
|
|
|
|
In general, when a format sets a pointer to a buffer, the buffer is
|
|
managed by the corresponding Python object, and the buffer shares
|
|
the lifetime of this object. You won't have to release any memory yourself.
|
|
The only exceptions are ``es``, ``es#``, ``et`` and ``et#``.
|
|
|
|
However, when a :c:type:`Py_buffer` structure gets filled, the underlying
|
|
buffer is locked so that the caller can subsequently use the buffer even
|
|
inside a :c:type:`Py_BEGIN_ALLOW_THREADS` block without the risk of mutable data
|
|
being resized or destroyed. As a result, **you have to call**
|
|
:c:func:`PyBuffer_Release` after you have finished processing the data (or
|
|
in any early abort case).
|
|
|
|
Unless otherwise stated, buffers are not NUL-terminated.
|
|
|
|
Some formats require a read-only :term:`bytes-like object`, and set a
|
|
pointer instead of a buffer structure. They work by checking that
|
|
the object's :c:member:`PyBufferProcs.bf_releasebuffer` field is *NULL*,
|
|
which disallows mutable objects such as :class:`bytearray`.
|
|
|
|
.. note::
|
|
|
|
For all ``#`` variants of formats (``s#``, ``y#``, etc.), the type of
|
|
the length argument (int or :c:type:`Py_ssize_t`) is controlled by
|
|
defining the macro :c:macro:`PY_SSIZE_T_CLEAN` before including
|
|
:file:`Python.h`. If the macro was defined, length is a
|
|
:c:type:`Py_ssize_t` rather than an :c:type:`int`. This behavior will change
|
|
in a future Python version to only support :c:type:`Py_ssize_t` and
|
|
drop :c:type:`int` support. It is best to always define :c:macro:`PY_SSIZE_T_CLEAN`.
|
|
|
|
|
|
``s`` (:class:`str`) [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 :exc:`ValueError` exception is raised. Unicode objects are converted
|
|
to C strings using ``'utf-8'`` encoding. If this conversion fails, a
|
|
:exc:`UnicodeError` is raised.
|
|
|
|
.. note::
|
|
This format does not accept :term:`bytes-like objects
|
|
<bytes-like object>`. If you want to accept
|
|
filesystem paths and convert them to C character strings, it is
|
|
preferable to use the ``O&`` format with :c:func:`PyUnicode_FSConverter`
|
|
as *converter*.
|
|
|
|
.. versionchanged:: 3.5
|
|
Previously, :exc:`TypeError` was raised when embedded null code points
|
|
were encountered in the Python string.
|
|
|
|
``s*`` (:class:`str` or :term:`bytes-like object`) [Py_buffer]
|
|
This format accepts Unicode objects as well as bytes-like objects.
|
|
It fills a :c:type:`Py_buffer` 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#`` (:class:`str`, read-only :term:`bytes-like object`) [const char \*, int or :c:type:`Py_ssize_t`]
|
|
Like ``s*``, except that it doesn't accept mutable objects.
|
|
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`` (:class:`str` 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*`` (:class:`str`, :term:`bytes-like object` or ``None``) [Py_buffer]
|
|
Like ``s*``, but the Python object may also be ``None``, in which case the
|
|
``buf`` member of the :c:type:`Py_buffer` structure is set to *NULL*.
|
|
|
|
``z#`` (:class:`str`, read-only :term:`bytes-like object` or ``None``) [const char \*, int]
|
|
Like ``s#``, but the Python object may also be ``None``, in which case the C
|
|
pointer is set to *NULL*.
|
|
|
|
``y`` (read-only :term:`bytes-like object`) [const char \*]
|
|
This format converts a bytes-like object to a C pointer to a character
|
|
string; it does not accept Unicode objects. The bytes buffer must not
|
|
contain embedded null bytes; if it does, a :exc:`ValueError`
|
|
exception is raised.
|
|
|
|
.. versionchanged:: 3.5
|
|
Previously, :exc:`TypeError` was raised when embedded null bytes were
|
|
encountered in the bytes buffer.
|
|
|
|
``y*`` (:term:`bytes-like object`) [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 :term:`bytes-like object`) [const char \*, int]
|
|
This variant on ``s#`` doesn't accept Unicode objects, only bytes-like
|
|
objects.
|
|
|
|
``S`` (:class:`bytes`) [PyBytesObject \*]
|
|
Requires that the Python object is a :class:`bytes` object, without
|
|
attempting any conversion. Raises :exc:`TypeError` if the object is not
|
|
a bytes object. The C variable may also be declared as :c:type:`PyObject\*`.
|
|
|
|
``Y`` (:class:`bytearray`) [PyByteArrayObject \*]
|
|
Requires that the Python object is a :class:`bytearray` object, without
|
|
attempting any conversion. Raises :exc:`TypeError` if the object is not
|
|
a :class:`bytearray` object. The C variable may also be declared as :c:type:`PyObject\*`.
|
|
|
|
``u`` (:class:`str`) [const Py_UNICODE \*]
|
|
Convert a Python Unicode object to a C pointer to a NUL-terminated buffer of
|
|
Unicode characters. You must pass the address of a :c:type:`Py_UNICODE`
|
|
pointer variable, which will be filled with the pointer to an existing
|
|
Unicode buffer. Please note that the width of a :c:type:`Py_UNICODE`
|
|
character depends on compilation options (it is either 16 or 32 bits).
|
|
The Python string must not contain embedded null code points; if it does,
|
|
a :exc:`ValueError` exception is raised.
|
|
|
|
.. versionchanged:: 3.5
|
|
Previously, :exc:`TypeError` was raised when embedded null code points
|
|
were encountered in the Python string.
|
|
|
|
.. deprecated-removed:: 3.3 4.0
|
|
Part of the old-style :c:type:`Py_UNICODE` API; please migrate to using
|
|
:c:func:`PyUnicode_AsWideCharString`.
|
|
|
|
``u#`` (:class:`str`) [const 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. This variant allows
|
|
null code points.
|
|
|
|
.. deprecated-removed:: 3.3 4.0
|
|
Part of the old-style :c:type:`Py_UNICODE` API; please migrate to using
|
|
:c:func:`PyUnicode_AsWideCharString`.
|
|
|
|
``Z`` (:class:`str` or ``None``) [const Py_UNICODE \*]
|
|
Like ``u``, but the Python object may also be ``None``, in which case the
|
|
:c:type:`Py_UNICODE` pointer is set to *NULL*.
|
|
|
|
.. deprecated-removed:: 3.3 4.0
|
|
Part of the old-style :c:type:`Py_UNICODE` API; please migrate to using
|
|
:c:func:`PyUnicode_AsWideCharString`.
|
|
|
|
``Z#`` (:class:`str` or ``None``) [const Py_UNICODE \*, int]
|
|
Like ``u#``, but the Python object may also be ``None``, in which case the
|
|
:c:type:`Py_UNICODE` pointer is set to *NULL*.
|
|
|
|
.. deprecated-removed:: 3.3 4.0
|
|
Part of the old-style :c:type:`Py_UNICODE` API; please migrate to using
|
|
:c:func:`PyUnicode_AsWideCharString`.
|
|
|
|
``U`` (:class:`str`) [PyObject \*]
|
|
Requires that the Python object is a Unicode object, without attempting
|
|
any conversion. Raises :exc:`TypeError` if the object is not a Unicode
|
|
object. The C variable may also be declared as :c:type:`PyObject\*`.
|
|
|
|
``w*`` (read-write :term:`bytes-like object`) [Py_buffer]
|
|
This format accepts any object which implements the read-write buffer
|
|
interface. It fills a :c:type:`Py_buffer` structure provided by the caller.
|
|
The buffer may contain embedded null bytes. The caller have to call
|
|
:c:func:`PyBuffer_Release` when it is done with the buffer.
|
|
|
|
``es`` (:class:`str`) [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 :c:type:`const char\*` 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 :c:type:`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.
|
|
|
|
:c:func:`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 :c:func:`PyMem_Free` to
|
|
free the allocated buffer after use.
|
|
|
|
``et`` (:class:`str`, :class:`bytes` or :class:`bytearray`) [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#`` (:class:`str`) [const char \*encoding, char \*\*buffer, int \*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
|
|
:c:type:`const char\*` 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 :c:type:`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
|
|
:c:func:`PyMem_Free` to free the allocated buffer after usage.
|
|
|
|
If *\*buffer* points to a non-*NULL* pointer (an already allocated buffer),
|
|
:c:func:`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 :exc:`ValueError` will be set.
|
|
|
|
In both cases, *\*buffer_length* is set to the length of the encoded data
|
|
without the trailing NUL byte.
|
|
|
|
``et#`` (:class:`str`, :class:`bytes` or :class:`bytearray`) [const char \*encoding, char \*\*buffer, int \*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.
|
|
|
|
Numbers
|
|
-------
|
|
|
|
``b`` (:class:`int`) [unsigned char]
|
|
Convert a nonnegative Python integer to an unsigned tiny int, stored in a C
|
|
:c:type:`unsigned char`.
|
|
|
|
``B`` (:class:`int`) [unsigned char]
|
|
Convert a Python integer to a tiny int without overflow checking, stored in a C
|
|
:c:type:`unsigned char`.
|
|
|
|
``h`` (:class:`int`) [short int]
|
|
Convert a Python integer to a C :c:type:`short int`.
|
|
|
|
``H`` (:class:`int`) [unsigned short int]
|
|
Convert a Python integer to a C :c:type:`unsigned short int`, without overflow
|
|
checking.
|
|
|
|
``i`` (:class:`int`) [int]
|
|
Convert a Python integer to a plain C :c:type:`int`.
|
|
|
|
``I`` (:class:`int`) [unsigned int]
|
|
Convert a Python integer to a C :c:type:`unsigned int`, without overflow
|
|
checking.
|
|
|
|
``l`` (:class:`int`) [long int]
|
|
Convert a Python integer to a C :c:type:`long int`.
|
|
|
|
``k`` (:class:`int`) [unsigned long]
|
|
Convert a Python integer to a C :c:type:`unsigned long` without
|
|
overflow checking.
|
|
|
|
``L`` (:class:`int`) [long long]
|
|
Convert a Python integer to a C :c:type:`long long`.
|
|
|
|
``K`` (:class:`int`) [unsigned long long]
|
|
Convert a Python integer to a C :c:type:`unsigned long long`
|
|
without overflow checking.
|
|
|
|
``n`` (:class:`int`) [Py_ssize_t]
|
|
Convert a Python integer to a C :c:type:`Py_ssize_t`.
|
|
|
|
``c`` (:class:`bytes` or :class:`bytearray` of length 1) [char]
|
|
Convert a Python byte, represented as a :class:`bytes` or
|
|
:class:`bytearray` object of length 1, to a C :c:type:`char`.
|
|
|
|
.. versionchanged:: 3.3
|
|
Allow :class:`bytearray` objects.
|
|
|
|
``C`` (:class:`str` of length 1) [int]
|
|
Convert a Python character, represented as a :class:`str` object of
|
|
length 1, to a C :c:type:`int`.
|
|
|
|
``f`` (:class:`float`) [float]
|
|
Convert a Python floating point number to a C :c:type:`float`.
|
|
|
|
``d`` (:class:`float`) [double]
|
|
Convert a Python floating point number to a C :c:type:`double`.
|
|
|
|
``D`` (:class:`complex`) [Py_complex]
|
|
Convert a Python complex number to a C :c:type:`Py_complex` structure.
|
|
|
|
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. The object's 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 :c:type:`PyObject\*`) into which
|
|
the object pointer is stored. If the Python object does not have the required
|
|
type, :exc:`TypeError` is raised.
|
|
|
|
.. _o_ampersand:
|
|
|
|
``O&`` (object) [*converter*, *anything*]
|
|
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 :c:type:`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
|
|
:c:type:`void\*` argument that was passed to the :c:func:`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``, 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.
|
|
|
|
.. versionchanged:: 3.1
|
|
``Py_CLEANUP_SUPPORTED`` was added.
|
|
|
|
``p`` (:class:`bool`) [int]
|
|
Tests the value passed in for truth (a boolean **p**\ redicate) 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 :ref:`truth` for more
|
|
information about how Python tests values for truth.
|
|
|
|
.. versionadded:: 3.3
|
|
|
|
``(items)`` (:class:`tuple`) [*matching-items*]
|
|
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.
|
|
|
|
It is possible to pass "long" integers (integers whose value exceeds the
|
|
platform's :const:`LONG_MAX`) 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:
|
|
|
|
``|``
|
|
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,
|
|
:c:func:`PyArg_ParseTuple` does not touch the contents of the corresponding C
|
|
variable(s).
|
|
|
|
``$``
|
|
:c:func:`PyArg_ParseTupleAndKeywords` only:
|
|
Indicates that the remaining arguments in the Python argument list are
|
|
keyword-only. Currently, all keyword-only arguments must also be optional
|
|
arguments, so ``|`` must always be specified before ``$`` 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
|
|
:c:func:`PyArg_ParseTuple` 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 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
|
|
:c:func:`PyArg_Parse\*` functions return true, otherwise they return
|
|
false and raise an appropriate exception. When the
|
|
:c:func:`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
|
|
-------------
|
|
|
|
.. c:function:: int PyArg_ParseTuple(PyObject *args, const char *format, ...)
|
|
|
|
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.
|
|
|
|
|
|
.. c:function:: int PyArg_VaParse(PyObject *args, const char *format, va_list vargs)
|
|
|
|
Identical to :c:func:`PyArg_ParseTuple`, except that it accepts a va_list rather
|
|
than a variable number of arguments.
|
|
|
|
|
|
.. c:function:: int PyArg_ParseTupleAndKeywords(PyObject *args, PyObject *kw, const char *format, char *keywords[], ...)
|
|
|
|
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. Empty names denote
|
|
:ref:`positional-only parameters <positional-only_parameter>`.
|
|
Returns true on success; on failure, it returns false and raises the
|
|
appropriate exception.
|
|
|
|
.. versionchanged:: 3.6
|
|
Added support for :ref:`positional-only parameters
|
|
<positional-only_parameter>`.
|
|
|
|
|
|
.. c:function:: int PyArg_VaParseTupleAndKeywords(PyObject *args, PyObject *kw, const char *format, char *keywords[], va_list vargs)
|
|
|
|
Identical to :c:func:`PyArg_ParseTupleAndKeywords`, except that it accepts a
|
|
va_list rather than a variable number of arguments.
|
|
|
|
|
|
.. c:function:: int PyArg_ValidateKeywordArguments(PyObject *)
|
|
|
|
Ensure that the keys in the keywords argument dictionary are strings. This
|
|
is only needed if :c:func:`PyArg_ParseTupleAndKeywords` is not used, since the
|
|
latter already does this check.
|
|
|
|
.. versionadded:: 3.2
|
|
|
|
|
|
.. XXX deprecated, will be removed
|
|
.. c:function:: int PyArg_Parse(PyObject *args, const char *format, ...)
|
|
|
|
Function used to deconstruct the argument lists of "old-style" functions ---
|
|
these are functions which use the :const:`METH_OLDARGS` parameter parsing
|
|
method, which has been removed in Python 3. This is not recommended for use
|
|
in parameter parsing in new code, and most code in the standard interpreter
|
|
has been modified to no longer use this for that purpose. It does remain a
|
|
convenient way to decompose other tuples, however, and may continue to be
|
|
used for that purpose.
|
|
|
|
|
|
.. c:function:: int PyArg_UnpackTuple(PyObject *args, const char *name, Py_ssize_t min, Py_ssize_t max, ...)
|
|
|
|
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 :const:`METH_VARARGS` 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
|
|
:c:type:`PyObject\*` variable; these will be filled in with the values from
|
|
*args*; they will contain borrowed references. 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
|
|
:mod:`_weakref` 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 :c:func:`PyArg_UnpackTuple` in this example is entirely equivalent to
|
|
this call to :c:func:`PyArg_ParseTuple`::
|
|
|
|
PyArg_ParseTuple(args, "O|O:ref", &object, &callback)
|
|
|
|
|
|
---------------
|
|
Building values
|
|
---------------
|
|
|
|
.. c:function:: PyObject* Py_BuildValue(const char *format, ...)
|
|
|
|
Create a new value based on a format string similar to those accepted by the
|
|
:c:func:`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.
|
|
|
|
:c:func:`Py_BuildValue` 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
|
|
:c:func:`Py_BuildValue`. In other words, if your code invokes :c:func:`malloc`
|
|
and passes the allocated memory to :c:func:`Py_BuildValue`, your code is
|
|
responsible for calling :c:func:`free` for that memory once
|
|
:c:func:`Py_BuildValue` 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`` (:class:`str` or ``None``) [const char \*]
|
|
Convert a null-terminated C string to a Python :class:`str` object using ``'utf-8'``
|
|
encoding. If the C string pointer is *NULL*, ``None`` is used.
|
|
|
|
``s#`` (:class:`str` or ``None``) [const char \*, int]
|
|
Convert a C string and its length to a Python :class:`str` object using ``'utf-8'``
|
|
encoding. If the C string pointer is *NULL*, the length is ignored and
|
|
``None`` is returned.
|
|
|
|
``y`` (:class:`bytes`) [const char \*]
|
|
This converts a C string to a Python :class:`bytes` object. If the C
|
|
string pointer is *NULL*, ``None`` is returned.
|
|
|
|
``y#`` (:class:`bytes`) [const char \*, int]
|
|
This converts a C string and its lengths to a Python object. If the C
|
|
string pointer is *NULL*, ``None`` is returned.
|
|
|
|
``z`` (:class:`str` or ``None``) [const char \*]
|
|
Same as ``s``.
|
|
|
|
``z#`` (:class:`str` or ``None``) [const char \*, int]
|
|
Same as ``s#``.
|
|
|
|
``u`` (:class:`str`) [const wchar_t \*]
|
|
Convert a null-terminated :c:type:`wchar_t` 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#`` (:class:`str`) [const wchar_t \*, int]
|
|
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`` (:class:`str` or ``None``) [const char \*]
|
|
Same as ``s``.
|
|
|
|
``U#`` (:class:`str` or ``None``) [const char \*, int]
|
|
Same as ``s#``.
|
|
|
|
``i`` (:class:`int`) [int]
|
|
Convert a plain C :c:type:`int` to a Python integer object.
|
|
|
|
``b`` (:class:`int`) [char]
|
|
Convert a plain C :c:type:`char` to a Python integer object.
|
|
|
|
``h`` (:class:`int`) [short int]
|
|
Convert a plain C :c:type:`short int` to a Python integer object.
|
|
|
|
``l`` (:class:`int`) [long int]
|
|
Convert a C :c:type:`long int` to a Python integer object.
|
|
|
|
``B`` (:class:`int`) [unsigned char]
|
|
Convert a C :c:type:`unsigned char` to a Python integer object.
|
|
|
|
``H`` (:class:`int`) [unsigned short int]
|
|
Convert a C :c:type:`unsigned short int` to a Python integer object.
|
|
|
|
``I`` (:class:`int`) [unsigned int]
|
|
Convert a C :c:type:`unsigned int` to a Python integer object.
|
|
|
|
``k`` (:class:`int`) [unsigned long]
|
|
Convert a C :c:type:`unsigned long` to a Python integer object.
|
|
|
|
``L`` (:class:`int`) [long long]
|
|
Convert a C :c:type:`long long` to a Python integer object.
|
|
|
|
``K`` (:class:`int`) [unsigned long long]
|
|
Convert a C :c:type:`unsigned long long` to a Python integer object.
|
|
|
|
``n`` (:class:`int`) [Py_ssize_t]
|
|
Convert a C :c:type:`Py_ssize_t` to a Python integer.
|
|
|
|
``c`` (:class:`bytes` of length 1) [char]
|
|
Convert a C :c:type:`int` representing a byte to a Python :class:`bytes` object of
|
|
length 1.
|
|
|
|
``C`` (:class:`str` of length 1) [int]
|
|
Convert a C :c:type:`int` representing a character to Python :class:`str`
|
|
object of length 1.
|
|
|
|
``d`` (:class:`float`) [double]
|
|
Convert a C :c:type:`double` to a Python floating point number.
|
|
|
|
``f`` (:class:`float`) [float]
|
|
Convert a C :c:type:`float` to a Python floating point number.
|
|
|
|
``D`` (:class:`complex`) [Py_complex \*]
|
|
Convert a C :c:type:`Py_complex` structure to a Python complex number.
|
|
|
|
``O`` (object) [PyObject \*]
|
|
Pass a Python object untouched (except for its reference count, which 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, :c:func:`Py_BuildValue` will return *NULL* but won't
|
|
raise an exception. If no exception has been raised yet, :exc:`SystemError` is
|
|
set.
|
|
|
|
``S`` (object) [PyObject \*]
|
|
Same as ``O``.
|
|
|
|
``N`` (object) [PyObject \*]
|
|
Same as ``O``, except it doesn't increment the reference count on the object.
|
|
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 :c:type:`void
|
|
\*`) as its argument and should return a "new" Python object, or *NULL* if an
|
|
error occurred.
|
|
|
|
``(items)`` (:class:`tuple`) [*matching-items*]
|
|
Convert a sequence of C values to a Python tuple with the same number of items.
|
|
|
|
``[items]`` (:class:`list`) [*matching-items*]
|
|
Convert a sequence of C values to a Python list with the same number of items.
|
|
|
|
``{items}`` (:class:`dict`) [*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 :exc:`SystemError` exception is
|
|
set and *NULL* returned.
|
|
|
|
.. c:function:: PyObject* Py_VaBuildValue(const char *format, va_list vargs)
|
|
|
|
Identical to :c:func:`Py_BuildValue`, except that it accepts a va_list
|
|
rather than a variable number of arguments.
|