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The __getslice__, __setslice__ and __delslice__ methods have been deprecated since Python 2.0. In general, no class should implement these methods.
The only exceptions to this rule are classes that inherit from list and override __getitem__, __setitem__ or __delitem__. Since list implements the slicing methods any class inheriting from list must implement the the slicing methods to ensure correct behavior of __getitem__, __setitem__ and __delitem__. These exceptions to the rule will not be treated as violations.
Delete the slicing method. Any functionality should be moved to the equivalent __xxxitem__ method:
__getslice__ should be replaced with __getitem__
__setslice__ should be replaced with __setitem__
__delslice__ should be replaced with __delitem__
Python Language Reference: Additional methods for emulation of sequence types.