1import unittest
2from ctypes import *
3
4class StructFieldsTestCase(unittest.TestCase):
5    # Structure/Union classes must get 'finalized' sooner or
6    # later, when one of these things happen:
7    #
8    # 1. _fields_ is set.
9    # 2. An instance is created.
10    # 3. The type is used as field of another Structure/Union.
11    # 4. The type is subclassed
12    #
13    # When they are finalized, assigning _fields_ is no longer allowed.
14
15    def test_1_A(self):
16        class X(Structure):
17            pass
18        self.assertEqual(sizeof(X), 0) # not finalized
19        X._fields_ = [] # finalized
20        self.assertRaises(AttributeError, setattr, X, "_fields_", [])
21
22    def test_1_B(self):
23        class X(Structure):
24            _fields_ = [] # finalized
25        self.assertRaises(AttributeError, setattr, X, "_fields_", [])
26
27    def test_2(self):
28        class X(Structure):
29            pass
30        X()
31        self.assertRaises(AttributeError, setattr, X, "_fields_", [])
32
33    def test_3(self):
34        class X(Structure):
35            pass
36        class Y(Structure):
37            _fields_ = [("x", X)] # finalizes X
38        self.assertRaises(AttributeError, setattr, X, "_fields_", [])
39
40    def test_4(self):
41        class X(Structure):
42            pass
43        class Y(X):
44            pass
45        self.assertRaises(AttributeError, setattr, X, "_fields_", [])
46        Y._fields_ = []
47        self.assertRaises(AttributeError, setattr, X, "_fields_", [])
48
49if __name__ == "__main__":
50    unittest.main()
51