def test_alias_delay_initialization1(capture): """`A` only initializes its trampoline class when we inherit from it If we just create and use an A instance directly, the trampoline initialization is bypassed and we only initialize an A() instead (for performance reasons). """ class B(m.A): def __init__(self): super(B, self).__init__() def f(self): print("In python f()") # C++ version with capture: a = m.A() m.call_f(a) del a pytest.gc_collect() assert capture == "A.f()" # Python version with capture: b = B() m.call_f(b) del b pytest.gc_collect() assert capture == """
def test_alias_delay_initialization2(capture): """`A2`, unlike the above, is configured to always initialize the alias While the extra initialization and extra class layer has small virtual dispatch performance penalty, it also allows us to do more things with the trampoline class such as defining local variables and performing construction/destruction. """ class B2(m.A2): def __init__(self): super(B2, self).__init__() def f(self): print("In python B2.f()") # No python subclass version with capture: a2 = m.A2() m.call_f(a2) del a2 pytest.gc_collect() assert capture == """ PyA2.PyA2() PyA2.f() A2.f() PyA2.~PyA2() """ # Python subclass version with capture: b2 = B2() m.call_f(b2) del b2 pytest.gc_collect() assert capture == """