import py from ctypes import * py.test.skip("subclassing semantics and implementation details not implemented") class X(Structure): _fields_ = [("a", c_int), ("b", c_int)] new_was_called = False def __new__(cls): result = super(X, cls).__new__(cls) result.new_was_called = True return result def __init__(self): self.a = 9 self.b = 12 class Y(Structure): _fields_ = [("x", X)] class TestInit: def test_get(self): # make sure the only accessing a nested structure # doesn't call the structure's __new__ and __init__ y = Y() assert (y.x.a, y.x.b) == (0, 0) assert y.x.new_was_called == False # But explicitely creating an X structure calls __new__ and __init__, of course. x = X() assert (x.a, x.b) == (9, 12) assert x.new_was_called == True y.x = x assert (y.x.a, y.x.b) == (9, 12) assert y.x.new_was_called == False