input: Write a python function to get the Q-value for a given state and action.
  assert QLearner().get_Q('state1', 'action1') == 0.0
  assert QLearner(alpha=0.5).get_Q('state2', 'action2') == 0.0
output: def QLearner(alpha=0.1, gamma=0.9):
      class _QLearner:
          def __init__(self):
              self.Q = {}
              self.alpha = alpha
              self.gamma = gamma
  
          def get_Q(self, state, action):
              return self.Q.get((state, action), 0.0)
  
      return _QLearner()