def compute_single_policy_backup(self, policy: Policy, gamma: float) -> Tuple[ValueFunction, float]:
'''
Performs a policy backup on the current value function
and using the specified policy.
This method does not modify the current value function;
instead it returns a new value function,
together with the error associated with the backup operation.
'''
# DONE
new_value_function = ValueFunction(self._domain)
error = 0
for state in self._domain.get_observation_space().get_elements():
if self._domain.is_terminal(state):
new_value_function._values[state] = 0
else:
action = policy.__getitem__(state)
# distribution = self._domain.get_next_state_distribution(state,action).get_values()
new_value_function._values[state] = self.q_value(state,action,gamma)
if error < abs(self.q_value(state,action,gamma) - self.__getitem__(state)):
error = abs(self.q_value(state,action,gamma) - self.__getitem__(state))
return new_value_function, error