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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 make_slice_key(cls, start_string, size_string):
 """ Converts the given start and size query parts to a slice key. :return: slice key :rtype: slice """

        try:
            start = int(start_string)
        except ValueError:
            raise ValueError('Query parameter "start" must be a number.')
        if start < 0:
            raise ValueError('Query parameter "start" must be zero or '
                             'a positive number.')
        try:
            size = int(size_string)
        except ValueError:
            raise ValueError('Query parameter "size" must be a number.')
        if size < 1:
            raise ValueError('Query parameter "size" must be a positive '
                             'number.')
        return slice(start, start + size)