`__getslice__` has been Deprecated since Python 2.0 and is removed in Python 3. See https://docs.python.org/2/reference/datamodel.html#object.__getslice__ Unfortunately, Python 2 will still dispatch to `__getslice__` over `__getitem__`, See http://bugs.python.org/issue2041, which causes Warnings when running with `-3` in 2.7.