Limiting the pointer-type cache could be a problem. It's expected that POINTER() returns a reference to an existing pointer type. ctypes uses Python types to ensure compatible C data types. For example:

    LP_c_int = ctypes.POINTER(ctypes.c_int)

    class LP_c_int_uncached(ctypes._Pointer):
        _type_ = ctypes.c_int

    >>> arr = (LP_c_int * 2)()
    >>> ctypes.POINTER(ctypes.c_int) is LP_c_int
    True
    >>> arr[0] = ctypes.POINTER(ctypes.c_int)()
    >>> arr[1] = LP_c_int_uncached()
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: incompatible types, LP_c_int_uncached instance
    instead of LP_c_int instance

The docs could warn users that the cache used by ctypes.POINTER(), and implicitly by ctypes.pointer(), will leak memory if it's called with a type that's created at function scope instead of at module or class-body scope.