consumer.committed([TopicPartition('test', 0)]) blocks and hangs about confluent-kafka-python HOT 9 CLOSED

def test_pos ():
    c = Consumer({"bootstrap.servers":"0",
                  "group.id":"xx3",
                  "enable.auto.commit":False,
                  "default.topic.config":{"auto.offset.reset":"earliest"}})

    c.subscribe(["test"])
    while True:
        m = c.poll(1)
        print(m)
        tp = TopicPartition("test", 0)
        cs = c.committed([tp])
        print('committed offsets for',tp, 'is', cs)

    c.close()

None
('committed offsets for', TopicPartition{topic=test,partition=0,offset=-1001,error=None}, 'is', [TopicPartition{topic=test,partition=0,offset=-1001,error=None}])
<cimpl.Message object at 0x7f1248b06fa0>
('committed offsets for', TopicPartition{topic=test,partition=0,offset=-1001,error=None}, 'is', [TopicPartition{topic=test,partition=0,offset=-1001,error=None}])
<cimpl.Message object at 0x7f1248ac0050>
...