casting an array to a pointer works array and p share a common objects attribute this didn t work bad argument to internal function the type argument must be a ctypes pointer type casting an array to a pointer works array and p share a common _objects attribute this didn t work bad argument to internal function the type argument must be a ctypes pointer type
import sys
import unittest
from ctypes import (Structure, Union, POINTER, cast, sizeof, addressof,
                    c_void_p, c_char_p, c_wchar_p,
                    c_byte, c_short, c_int)


class Test(unittest.TestCase):
    def test_array2pointer(self):
        array = (c_int * 3)(42, 17, 2)

        
        ptr = cast(array, POINTER(c_int))
        self.assertEqual([ptr[i] for i in range(3)], [42, 17, 2])

        if 2 * sizeof(c_short) == sizeof(c_int):
            ptr = cast(array, POINTER(c_short))
            if sys.byteorder == "little":
                self.assertEqual([ptr[i] for i in range(6)],
                                     [42, 0, 17, 0, 2, 0])
            else:
                self.assertEqual([ptr[i] for i in range(6)],
                                     [0, 42, 0, 17, 0, 2])

    def test_address2pointer(self):
        array = (c_int * 3)(42, 17, 2)

        address = addressof(array)
        ptr = cast(c_void_p(address), POINTER(c_int))
        self.assertEqual([ptr[i] for i in range(3)], [42, 17, 2])

        ptr = cast(address, POINTER(c_int))
        self.assertEqual([ptr[i] for i in range(3)], [42, 17, 2])

    def test_p2a_objects(self):
        array = (c_char_p * 5)()
        self.assertEqual(array._objects, None)
        array[0] = b"foo bar"
        self.assertEqual(array._objects, {'0': b"foo bar"})

        p = cast(array, POINTER(c_char_p))
        
        self.assertIs(p._objects, array._objects)
        self.assertEqual(array._objects, {'0': b"foo bar", id(array): array})
        p[0] = b"spam spam"
        self.assertEqual(p._objects, {'0': b"spam spam", id(array): array})
        self.assertIs(array._objects, p._objects)
        p[1] = b"foo bar"
        self.assertEqual(p._objects, {'1': b'foo bar', '0': b"spam spam", id(array): array})
        self.assertIs(array._objects, p._objects)

    def test_other(self):
        p = cast((c_int * 4)(1, 2, 3, 4), POINTER(c_int))
        self.assertEqual(p[:4], [1,2, 3, 4])
        self.assertEqual(p[:4:], [1, 2, 3, 4])
        self.assertEqual(p[3:-1:-1], [4, 3, 2, 1])
        self.assertEqual(p[:4:3], [1, 4])
        c_int()
        self.assertEqual(p[:4], [1, 2, 3, 4])
        self.assertEqual(p[:4:], [1, 2, 3, 4])
        self.assertEqual(p[3:-1:-1], [4, 3, 2, 1])
        self.assertEqual(p[:4:3], [1, 4])
        p[2] = 96
        self.assertEqual(p[:4], [1, 2, 96, 4])
        self.assertEqual(p[:4:], [1, 2, 96, 4])
        self.assertEqual(p[3:-1:-1], [4, 96, 2, 1])
        self.assertEqual(p[:4:3], [1, 4])
        c_int()
        self.assertEqual(p[:4], [1, 2, 96, 4])
        self.assertEqual(p[:4:], [1, 2, 96, 4])
        self.assertEqual(p[3:-1:-1], [4, 96, 2, 1])
        self.assertEqual(p[:4:3], [1, 4])

    def test_char_p(self):
        
        s = c_char_p(b"hiho")
        self.assertEqual(cast(cast(s, c_void_p), c_char_p).value,
                             b"hiho")

    def test_wchar_p(self):
        s = c_wchar_p("hiho")
        self.assertEqual(cast(cast(s, c_void_p), c_wchar_p).value,
                         "hiho")

    def test_bad_type_arg(self):
        
        array_type = c_byte * sizeof(c_int)
        array = array_type()
        self.assertRaises(TypeError, cast, array, None)
        self.assertRaises(TypeError, cast, array, array_type)
        class Struct(Structure):
            _fields_ = [("a", c_int)]
        self.assertRaises(TypeError, cast, array, Struct)
        class MyUnion(Union):
            _fields_ = [("a", c_int)]
        self.assertRaises(TypeError, cast, array, MyUnion)


if __name__ == "__main__":
    unittest.main()