Search for all subjects related to the specified predicate and object.

        :param predicate:
        :param object:
        :rtype: generator of RDF statements

def get_subjects(self, predicate, object):
        """
        Search for all subjects related to the specified predicate and object.

        :param predicate:
        :param object:
        :rtype: generator of RDF statements
        """
        for statement in self.spo_search(predicate=predicate, object=object):
            yield str(statement[0])