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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def slice(self, start=None, stop=None, step=None):
 """Slice substrings from each element. Note that negative step is currently not supported. Parameters start : int stop : int step : int Returns ------- Series """

        check_type(start, int)
        check_type(stop, int)
        check_type(step, int)

        if step is not None and step < 0:
            raise ValueError('Only positive steps are currently supported')

        return _series_str_result(self, weld_str_slice, start=start, stop=stop, step=step)