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      1 from ctypes import *
      2 import unittest
      3 
      4 class X(Structure):
      5     _fields_ = [("a", c_int),
      6                 ("b", c_int)]
      7     new_was_called = False
      8 
      9     def __new__(cls):
     10         result = super(X, cls).__new__(cls)
     11         result.new_was_called = True
     12         return result
     13 
     14     def __init__(self):
     15         self.a = 9
     16         self.b = 12
     17 
     18 class Y(Structure):
     19     _fields_ = [("x", X)]
     20 
     21 
     22 class InitTest(unittest.TestCase):
     23     def test_get(self):
     24         # make sure the only accessing a nested structure
     25         # doesn't call the structure's __new__ and __init__
     26         y = Y()
     27         self.assertEqual((y.x.a, y.x.b), (0, 0))
     28         self.assertEqual(y.x.new_was_called, False)
     29 
     30         # But explicitly creating an X structure calls __new__ and __init__, of course.
     31         x = X()
     32         self.assertEqual((x.a, x.b), (9, 12))
     33         self.assertEqual(x.new_was_called, True)
     34 
     35         y.x = x
     36         self.assertEqual((y.x.a, y.x.b), (9, 12))
     37         self.assertEqual(y.x.new_was_called, False)
     38 
     39 if __name__ == "__main__":
     40     unittest.main()
     41