Using f-strings for exception strings

ml-agents-envs/mlagents_envs/environment.py

         if launch_string is None:
             self._close()
             raise UnityEnvironmentException(
-                "Couldn't launch the {0} environment. "
-                "Provided filename does not match any environments.".format(file_name)
+                f"Couldn't launch the {file_name} environment. Provided filename does not match any environments."
             )
         else:
             logger.debug("This is the launch string {}".format(launch_string))
         self._env_actions[agent_group] = action
 
     def set_action_for_agent(
-            self, agent_group: AgentGroup, agent_id: AgentId, action: np.ndarray
+        self, agent_group: AgentGroup, agent_id: AgentId, action: np.ndarray
     ) -> None:
         self._assert_group_exists(agent_group)
         if agent_group not in self._env_state:
 
     @timed
     def _generate_step_input(
-            self, vector_action: Dict[str, np.ndarray]
+        self, vector_action: Dict[str, np.ndarray]
     ) -> UnityInputProto:
         rl_in = UnityRLInputProto()
         for b in vector_action:
         return self.wrap_unity_input(rl_in)
 
     def send_academy_parameters(
-            self, init_parameters: UnityRLInitializationInputProto
+        self, init_parameters: UnityRLInitializationInputProto
     ) -> UnityOutputProto:
         inputs = UnityInputProto()
         inputs.rl_initialization_input.CopyFrom(init_parameters)

ml-agents/mlagents/trainers/learn.py

         launch_string = UnityEnvironment.validate_environment_path(env_path)
         if launch_string is None:
             raise UnityEnvironmentException(
-                "Couldn't launch the {0} environment. "
-                "Provided filename does not match any environments.".format(env_path)
+                f"Couldn't launch the {env_path} environment. Provided filename does not match any environments."
             )
     docker_training = docker_target_name is not None
     if docker_training and env_path is not None: