python - 带有 Python 的 Cassandra 3.7， 'NoneType' 对象没有属性 'encode_message'

Question

我有一个简单的 python 客户端来从 cassandra 获取数据。查询字符串本身使用 DBeaver EE 客户端运行良好。

def getDataSet(self, station_id, tablename):
    prepared_stmt = self.session.prepare ( "SELECT event_time, reading FROM " +
                                           tablename + " WHERE station_id = ?;")
    bound_stmt = prepared_stmt.bind([station_id])
    rslt = self.session.execute(bound_stmt)
    df = pd.DataFrame()
    for r in rslt:
        df = df.append(r)
    return df

def __init__(self):
    cluster = Cluster(
        contact_points=['127.0.0.1'],
        )
    self.session = cluster.connect('data')
    self.session.row_factory = tuple_factory
    self.session.client_protocol_handler = NumpyProtocolHandler

我得到以下异常

File "/home/david/git/python-example/src/start/fetchcassandra.py", line 13, in getDataSet
rslt = self.session.execute(bound_stmt)
File "/usr/local/lib/python3.4/dist-packages/cassandra/cluster.py", line 1961, in execute
return self.execute_async(query, parameters, trace, custom_payload, timeout, execution_profile).result()
File "/usr/local/lib/python3.4/dist-packages/cassandra/cluster.py", line 3649, in result
raise self._final_exception
cassandra.cluster.NoHostAvailable: ('Unable to complete the operation against any hosts', {<Host: 127.0.0.1 datacenter1>: AttributeError("'NoneType' object has no attribute 'encode_message'",)})

Answer 1

很可能未构建 NumpyProtocolHander，因此您将指定 None 作为协议(protocol)处理程序。

参见 here有关安装说明，并查阅您的 pip 日志以获取有关未构建它的原因的线索。