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[3.13] gh-120313: amend documentation regarding ctypes._CFuncPtr (GH-120989) #125979

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[3.13] gh-120313: amend documentation regarding ctypes._CFuncPtr (GH-120989) #125979

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48 changes: 29 additions & 19 deletions Doc/library/ctypes.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -383,15 +383,15 @@ as calling functions with a fixed number of parameters. On some platforms, and i
particular ARM64 for Apple Platforms, the calling convention for variadic functions
is different than that for regular functions.

On those platforms it is required to specify the :attr:`~_FuncPtr.argtypes`
On those platforms it is required to specify the :attr:`~_CFuncPtr.argtypes`
attribute for the regular, non-variadic, function arguments:

.. code-block:: python3

libc.printf.argtypes = [ctypes.c_char_p]

Because specifying the attribute does not inhibit portability it is advised to always
specify :attr:`~_FuncPtr.argtypes` for all variadic functions.
specify :attr:`~_CFuncPtr.argtypes` for all variadic functions.


.. _ctypes-calling-functions-with-own-custom-data-types:
Expand Down Expand Up @@ -426,9 +426,9 @@ Specifying the required argument types (function prototypes)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

It is possible to specify the required argument types of functions exported from
DLLs by setting the :attr:`~_FuncPtr.argtypes` attribute.
DLLs by setting the :attr:`~_CFuncPtr.argtypes` attribute.

:attr:`~_FuncPtr.argtypes` must be a sequence of C data types (the :func:`!printf` function is
:attr:`~_CFuncPtr.argtypes` must be a sequence of C data types (the :func:`!printf` function is
probably not a good example here, because it takes a variable number and
different types of parameters depending on the format string, on the other hand
this is quite handy to experiment with this feature)::
Expand All @@ -453,7 +453,7 @@ prototype for a C function), and tries to convert the arguments to valid types::

If you have defined your own classes which you pass to function calls, you have
to implement a :meth:`~_CData.from_param` class method for them to be able to use them
in the :attr:`~_FuncPtr.argtypes` sequence. The :meth:`~_CData.from_param` class method receives
in the :attr:`~_CFuncPtr.argtypes` sequence. The :meth:`~_CData.from_param` class method receives
the Python object passed to the function call, it should do a typecheck or
whatever is needed to make sure this object is acceptable, and then return the
object itself, its :attr:`!_as_parameter_` attribute, or whatever you want to
Expand All @@ -476,7 +476,7 @@ Return types


By default functions are assumed to return the C :c:expr:`int` type. Other
return types can be specified by setting the :attr:`~_FuncPtr.restype` attribute of the
return types can be specified by setting the :attr:`~_CFuncPtr.restype` attribute of the
function object.

The C prototype of :c:func:`time` is ``time_t time(time_t *)``. Because :c:type:`time_t`
Expand All @@ -485,7 +485,7 @@ specify the :attr:`!restype` attribute::

>>> libc.time.restype = c_time_t

The argument types can be specified using :attr:`~_FuncPtr.argtypes`::
The argument types can be specified using :attr:`~_CFuncPtr.argtypes`::

>>> libc.time.argtypes = (POINTER(c_time_t),)

Expand All @@ -508,7 +508,7 @@ a string pointer and a char, and returns a pointer to a string::
>>>

If you want to avoid the :func:`ord("x") <ord>` calls above, you can set the
:attr:`~_FuncPtr.argtypes` attribute, and the second argument will be converted from a
:attr:`~_CFuncPtr.argtypes` attribute, and the second argument will be converted from a
single character Python bytes object into a C char:

.. doctest::
Expand All @@ -527,7 +527,7 @@ single character Python bytes object into a C char:
>>>

You can also use a callable Python object (a function or a class for example) as
the :attr:`~_FuncPtr.restype` attribute, if the foreign function returns an integer. The
the :attr:`~_CFuncPtr.restype` attribute, if the foreign function returns an integer. The
callable will be called with the *integer* the C function returns, and the
result of this call will be used as the result of your function call. This is
useful to check for error return values and automatically raise an exception::
Expand Down Expand Up @@ -555,7 +555,7 @@ get the string representation of an error code, and *returns* an exception.
:func:`GetLastError` to retrieve it.

Please note that a much more powerful error checking mechanism is available
through the :attr:`~_FuncPtr.errcheck` attribute;
through the :attr:`~_CFuncPtr.errcheck` attribute;
see the reference manual for details.


Expand Down Expand Up @@ -859,7 +859,7 @@ Type conversions
^^^^^^^^^^^^^^^^

Usually, ctypes does strict type checking. This means, if you have
``POINTER(c_int)`` in the :attr:`~_FuncPtr.argtypes` list of a function or as the type of
``POINTER(c_int)`` in the :attr:`~_CFuncPtr.argtypes` list of a function or as the type of
a member field in a structure definition, only instances of exactly the same
type are accepted. There are some exceptions to this rule, where ctypes accepts
other objects. For example, you can pass compatible array instances instead of
Expand All @@ -880,7 +880,7 @@ pointer types. So, for ``POINTER(c_int)``, ctypes accepts an array of c_int::
>>>

In addition, if a function argument is explicitly declared to be a pointer type
(such as ``POINTER(c_int)``) in :attr:`~_FuncPtr.argtypes`, an object of the pointed
(such as ``POINTER(c_int)``) in :attr:`~_CFuncPtr.argtypes`, an object of the pointed
type (``c_int`` in this case) can be passed to the function. ctypes will apply
the required :func:`byref` conversion in this case automatically.

Expand Down Expand Up @@ -1609,10 +1609,20 @@ As explained in the previous section, foreign functions can be accessed as
attributes of loaded shared libraries. The function objects created in this way
by default accept any number of arguments, accept any ctypes data instances as
arguments, and return the default result type specified by the library loader.
They are instances of a private class:

They are instances of a private local class :class:`!_FuncPtr` (not exposed
in :mod:`!ctypes`) which inherits from the private :class:`_CFuncPtr` class:

.. class:: _FuncPtr
.. doctest::

>>> import ctypes
>>> lib = ctypes.CDLL(None)
>>> issubclass(lib._FuncPtr, ctypes._CFuncPtr)
True
>>> lib._FuncPtr is ctypes._CFuncPtr
False

.. class:: _CFuncPtr

Base class for C callable foreign functions.

Expand Down Expand Up @@ -1778,7 +1788,7 @@ different ways, depending on the type and number of the parameters in the call:
The optional *paramflags* parameter creates foreign function wrappers with much
more functionality than the features described above.

*paramflags* must be a tuple of the same length as :attr:`~_FuncPtr.argtypes`.
*paramflags* must be a tuple of the same length as :attr:`~_CFuncPtr.argtypes`.

Each item in this tuple contains further information about a parameter, it must
be a tuple containing one, two, or three items.
Expand Down Expand Up @@ -1849,7 +1859,7 @@ value if there is a single one, or a tuple containing the output parameter
values when there are more than one, so the GetWindowRect function now returns a
RECT instance, when called.

Output parameters can be combined with the :attr:`~_FuncPtr.errcheck` protocol to do
Output parameters can be combined with the :attr:`~_CFuncPtr.errcheck` protocol to do
further output processing and error checking. The win32 ``GetWindowRect`` api
function returns a ``BOOL`` to signal success or failure, so this function could
do the error checking, and raises an exception when the api call failed::
Expand All @@ -1862,7 +1872,7 @@ do the error checking, and raises an exception when the api call failed::
>>> GetWindowRect.errcheck = errcheck
>>>

If the :attr:`~_FuncPtr.errcheck` function returns the argument tuple it receives
If the :attr:`~_CFuncPtr.errcheck` function returns the argument tuple it receives
unchanged, :mod:`ctypes` continues the normal processing it does on the output
parameters. If you want to return a tuple of window coordinates instead of a
``RECT`` instance, you can retrieve the fields in the function and return them
Expand Down Expand Up @@ -2162,7 +2172,7 @@ Data types

This method adapts *obj* to a ctypes type. It is called with the actual
object used in a foreign function call when the type is present in the
foreign function's :attr:`~_FuncPtr.argtypes` tuple;
foreign function's :attr:`~_CFuncPtr.argtypes` tuple;
it must return an object that can be used as a function call parameter.

All ctypes data types have a default implementation of this classmethod
Expand Down Expand Up @@ -2228,7 +2238,7 @@ Fundamental data types
Fundamental data types, when returned as foreign function call results, or, for
example, by retrieving structure field members or array items, are transparently
converted to native Python types. In other words, if a foreign function has a
:attr:`~_FuncPtr.restype` of :class:`c_char_p`, you will always receive a Python bytes
:attr:`~_CFuncPtr.restype` of :class:`c_char_p`, you will always receive a Python bytes
object, *not* a :class:`c_char_p` instance.

.. XXX above is false, it actually returns a Unicode string
Expand Down
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