test_descr.py 文件源码

def test_mutable_bases_with_failing_mro(self):
        # Testing mutable bases with failing mro...
        class WorkOnce(type):
            def __new__(self, name, bases, ns):
                self.flag = 0
                return super(WorkOnce, self).__new__(WorkOnce, name, bases, ns)
            def mro(self):
                if self.flag > 0:
                    raise RuntimeError, "bozo"
                else:
                    self.flag += 1
                    return type.mro(self)

        class WorkAlways(type):
            def mro(self):
                # this is here to make sure that .mro()s aren't called
                # with an exception set (which was possible at one point).
                # An error message will be printed in a debug build.
                # What's a good way to test for this?
                return type.mro(self)

        class C(object):
            pass

        class C2(object):
            pass

        class D(C):
            pass

        class E(D):
            pass

        class F(D):
            __metaclass__ = WorkOnce

        class G(D):
            __metaclass__ = WorkAlways

        # Immediate subclasses have their mro's adjusted in alphabetical
        # order, so E's will get adjusted before adjusting F's fails.  We
        # check here that E's gets restored.

        E_mro_before = E.__mro__
        D_mro_before = D.__mro__

        try:
            D.__bases__ = (C2,)
        except RuntimeError:
            self.assertEqual(E.__mro__, E_mro_before)
            self.assertEqual(D.__mro__, D_mro_before)
        else:
            self.fail("exception not propagated")