python - Cassandra: 'unicode' does not have the buffer interface -

i try use these both prepared statements in django app:

readings = "select * readings" readings_by_user_id = "select * readings user_id=?" 

i query against db with:

def get_all(self):     query = self.session.prepare(ps.all_readings)     all_readings = self.session.execute(query)      return all_readings  def get_all_by_user_id(self, user_id):     query = self.session.prepare(ps.readings_by_user_id)     readings = self.session.execute(query, [user_id])      return readings 

the first of both works pretty well. second gives me:

error 2015-07-08 09:42:56,634 | views::exception_handler 47 | ('unable complete operation against hosts', {<host: localhost data1>: typeerror("'unicode' not have buffer interface",)}) 

can tell me happened here? understand, there must unicode string somewhere not have buffer interface. string meant? prepared statement?

here stacktrace in addition:

   traceback (most recent call last):   file "/library/frameworks/python.framework/versions/2.7/lib/python2.7/site-packages/rest_framework/views.py", line 448, in dispatch     response = handler(request, *args, **kwargs)   file "/users/me/workspace/project/readings/views.py", line 36, in get_by_user_id     readings = self.tr_dao.get_all_by_user_id(user_id)   file "/users/me/workspace/project/readings/dao.py", line 22, in get_all_by_user_id     readings = self.session.execute(query, [user_id], timeout=60)   file "/library/frameworks/python.framework/versions/2.7/lib/python2.7/site-packages/cassandra/cluster.py", line 1405, in execute     result = future.result(timeout)   file "/library/frameworks/python.framework/versions/2.7/lib/python2.7/site-packages/cassandra/cluster.py", line 2967, in result     raise self._final_exception 

if on python 2 fix it

def get_all_by_user_id(self, user_id):     query = self.session.prepare(ps.readings_by_user_id)     readings = self.session.execute(query, [str(user_id)])     return readings