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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 add_key_filters(self, key_filters):
 """ Adds key filters to the inputs. :param key_filters: a list of filters :type key_filters: list :rtype: :class:`RiakMapReduce` """

        if self._input_mode == 'query':
            raise ValueError('Key filters are not supported in a query.')

        self._key_filters.extend(key_filters)
        return self