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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 search_call_sets(self, variant_set_id, name=None, biosample_id=None):
 """ Returns an iterator over the CallSets fulfilling the specified conditions from the specified VariantSet. :param str variant_set_id: Find callsets belonging to the provided variant set. :param str name: Only CallSets matching the specified name will be returned. :param str biosample_id: Only CallSets matching this id will be returned. :return: An iterator over the :class:`ga4gh.protocol.CallSet` objects defined by the query parameters. """

        request = protocol.SearchCallSetsRequest()
        request.variant_set_id = variant_set_id
        request.name = pb.string(name)
        request.biosample_id = pb.string(biosample_id)
        request.page_size = pb.int(self._page_size)
        return self._run_search_request(
            request, "callsets", protocol.SearchCallSetsResponse)