gh-120313: amend documentation regarding `ctypes._CFuncPtr` (GH-120989)

improve docs

Doc/library/ctypes.rst

@@ -397,7 +397,7 @@ 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
@@ -405,7 +405,7 @@ attribute for the regular, non-variadic, function arguments:
    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:
@@ -440,9 +440,9 @@ 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)::
@@ -467,7 +467,7 @@ 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
@@ -490,7 +490,7 @@ 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`
@@ -499,7 +499,7 @@ 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),)
 
@@ -522,7 +522,7 @@ 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::
@@ -541,7 +541,7 @@ 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::
@@ -569,7 +569,7 @@ 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.
 
 
@@ -877,7 +877,7 @@ 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
@@ -898,7 +898,7 @@ 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.
 
@@ -1627,10 +1627,20 @@ 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.
 
@@ -1796,7 +1806,7 @@ 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.
@@ -1867,7 +1877,7 @@ 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::
@@ -1880,7 +1890,7 @@ 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
@@ -2180,7 +2190,7 @@ 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
@@ -2246,7 +2256,7 @@ 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