深度递归

class A:
    pass
class B(A):
    pass
class C(A):
    pass
class D(B, C):
    pass
class E:
    pass
class F(D, E):
    pass
class G(F, D):
    pass
class I:
    pass
class J(B, C):
    pass
class K(A):
    pass
class H(I, J, K):
    pass
class Foo(H, G):
    pass