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Lib/ctypes/test/test_frombuffer.py
from ctypes import *
import array
import gc
import unittest

class X(Structure):
    _fields_ = [("c_int", c_int)]
    init_called = False
    def __init__(self):
        self._init_called = True

class Test(unittest.TestCase):
    def test_fom_buffer(self):
        a = array.array("i", range(16))
        x = (c_int * 16).from_buffer(a)

        y = X.from_buffer(a)
        self.assertEqual(y.c_int, a[0])
        self.assertFalse(y.init_called)

        self.assertEqual(x[:], a.tolist())

        a[0], a[-1] = 200, -200
        self.assertEqual(x[:], a.tolist())

        self.assertIn(a, x._objects.values())

        self.assertRaises(ValueError,
                          c_int.from_buffer, a, -1)

        expected = x[:]
        del a; gc.collect(); gc.collect(); gc.collect()
        self.assertEqual(x[:], expected)

        self.assertRaises(TypeError,
                          (c_char * 16).from_buffer, "a" * 16)

    def test_fom_buffer_with_offset(self):
        a = array.array("i", range(16))
        x = (c_int * 15).from_buffer(a, sizeof(c_int))

        self.assertEqual(x[:], a.tolist()[1:])
        self.assertRaises(ValueError, lambda: (c_int * 16).from_buffer(a, sizeof(c_int)))
        self.assertRaises(ValueError, lambda: (c_int * 1).from_buffer(a, 16 * sizeof(c_int)))

    def test_from_buffer_copy(self):
        a = array.array("i", range(16))
        x = (c_int * 16).from_buffer_copy(a)

        y = X.from_buffer_copy(a)
        self.assertEqual(y.c_int, a[0])
        self.assertFalse(y.init_called)

        self.assertEqual(x[:], range(16))

        a[0], a[-1] = 200, -200
        self.assertEqual(x[:], range(16))

        self.assertEqual(x._objects, None)

        self.assertRaises(ValueError,
                          c_int.from_buffer, a, -1)

        del a; gc.collect(); gc.collect(); gc.collect()
        self.assertEqual(x[:], range(16))

        x = (c_char * 16).from_buffer_copy("a" * 16)
        self.assertEqual(x[:], "a" * 16)

    def test_fom_buffer_copy_with_offset(self):
        a = array.array("i", range(16))
        x = (c_int * 15).from_buffer_copy(a, sizeof(c_int))

        self.assertEqual(x[:], a.tolist()[1:])
        self.assertRaises(ValueError,
                          (c_int * 16).from_buffer_copy, a, sizeof(c_int))
        self.assertRaises(ValueError,
                          (c_int * 1).from_buffer_copy, a, 16 * sizeof(c_int))

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