cython

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cdef class Base0:
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    pass
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cdef class Base(Base0):
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    pass
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cdef class Foo(Base):
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   cdef fooit(self):
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       return 42
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cdef class Bar(Foo):
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   pass
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cdef class Bam(Bar):
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   pass
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cdef class Zoo(Bam):
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   pass
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def fooit(Foo foo):
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    """
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    >>> zoo = Zoo()
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    >>> for cl in (Zoo, Bam, Bar, Foo, Base, Base0): assert isinstance(zoo, cl)
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    >>> fooit(zoo)
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    42
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    >>> bam = Bam()
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    >>> for cl in (Bam, Bar, Foo, Base, Base0): assert isinstance(bam, cl)
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    >>> fooit(bam)
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    42
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    >>> bar = Bar()
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    >>> for cl in (Bar, Foo, Base, Base0): assert isinstance(bar, cl)
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    >>> fooit(bar)
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    42
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    >>> foo = Foo()
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    >>> for cl in (Foo, Base, Base0): assert isinstance(foo, cl)
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    >>> fooit(foo)
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    42
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    >>> base = Base()
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    >>> for cl in (Base, Base0): assert isinstance(base, cl)
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    >>> fooit(base)
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    Traceback (most recent call last):
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    TypeError: Argument 'foo' has incorrect type (expected subclasses.Foo, got subclasses.Base)
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    >>> base0 = Base0()
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    >>> for cl in (Base0,): assert isinstance(base0, cl)
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    >>> fooit(base0)
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    Traceback (most recent call last):
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    TypeError: Argument 'foo' has incorrect type (expected subclasses.Foo, got subclasses.Base0)
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    """
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    return foo.fooit()
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