human
I wrote the below code

    global setVal
    class OldStyle:
        def __delitem__(self, index):
            global setVal
            setVal = index
    class OldStyleWithLen:
        def __delitem__(self, index):
            global setVal
            setVal = index
        def __len__(self):
            return 10
    class NewStyle(object, ):
        def __delitem__(self, index):
            global setVal
            setVal = index
    class OldStyleWithLenAndGetSlice:
        def __delitem__(self, index):
            global setVal
            setVal = index
        def __len__(self):
            return 10
        def __delslice__(self, start, stop):
            global setVal
            setVal = (start, stop)
    del NewStyle()[slice(None, (-1), None)]
    AreEqual(setVal, slice(None, (-1), None))
    del OldStyleWithLen()[slice(None, (-1), None)]
    AreEqual(setVal, slice(None, (-1), None))
    del OldStyle()[slice(None, (-1), None)]
    AreEqual(setVal, slice(None, (-1), None))
    del OldStyleWithLenAndGetSlice()[slice(None, (-1), None)]
    AreEqual(setVal, slice(None, (-1), None))
    del NewStyle()[:(-1)]
    AreEqual(setVal, slice(None, (-1), None))
    del OldStyleWithLen()[:(-1)]
    AreEqual(setVal, slice(0, 9, None))
    del OldStyleWithLenAndGetSlice()[:(-1)]
    AreEqual(setVal, (0, 9))
    del OldStyle()[:(-1):1]
    AreEqual(setVal, slice(None, (-1), 1))
    try:
        OldStyle()[:(-1)] = 123
        AssertUnreachable()
    except AttributeError:
        pass
    try:
        OldStyle()[(-1):] = 123
        AssertUnreachable()
    except AttributeError:
        pass
    del OldStyle()[:(-1):None]
    AreEqual(setVal, slice(None, (-1), None))
    del OldStyle()[(-1)::None]
    AreEqual(setVal, slice((-1), None, None))
    del OldStyle()[:(-1):None]
    AreEqual(setVal, slice(None, (-1), None))
    del OldStyle()[(-1)::None]
    AreEqual(setVal, slice((-1), None, None))

What's a good function header?
 ... Here's a good function header?
assistant
#Here's a good function header.

def test_oldclass_and_direct_delete():