Question: I have just started learning OpenAI gymnasium and started with CartPole-v1. Being new I was following a YouTube tutorial;  video:https://www.youtube.com/watch?v=Mut_u40Sqz4&t=2076s  (I am up to 1:08:22) and I also wanted to see a window of the game. However when running the code, Python threw this error: Traceback (most recent call last): File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/gymnasium/envs/classic_control/cartpole.py", line 223, in render import pygame ModuleNotFoundError: No module named 'pygame' The above exception was the direct cause of the following exception: Traceback (most recent call last): File "/Users/artemnikoan/Documents/CartPole-v1.py", line 9, in <module> state = env.reset() File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/gymnasium/wrappers/time_limit.py", line 75, in reset return self.env.reset(**kwargs) File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/gymnasium/wrappers/order_enforcing.py", line 61, in reset return self.env.reset(**kwargs) File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/gymnasium/wrappers/env_checker.py", line 57, in reset return env_reset_passive_checker(self.env, **kwargs) File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/gymnasium/utils/passive_env_checker.py", line 186, in env_reset_passive_checker result = env.reset(**kwargs) File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/gymnasium/envs/classic_control/cartpole.py", line 209, in reset self.render() File "/Library/Frameworks/Python.framework/Versions/3.11/lib/python3.11/site-packages/gymnasium/envs/classic_control/cartpole.py", line 226, in render raise DependencyNotInstalled( gymnasium.error.DependencyNotInstalled: pygame is not installed, run `pip install gymnasium[classic-control]`  I made sure pygame and gymnasium classic-control are installed, but it still didn't work.  Here is the code: import os import gymnasium as gym from stable_baselines3 import PPO from stable_baselines3.common.vec_env import DummyVecEnv from stable_baselines3.common.evaluation import evaluate_policy env=gym.make('CartPole-v1',render_mode='human') episodes = 5 for episode in range(1, episodes+1): state = env.reset() done = False score = 0 while not done: env.render() action = env.action_space.sample() n_state, reward, done, truncated, info = env.step(action) score+=reward print('Episode:{} Score:{}'.format(episode, score)) env.close() log_path=os.path.join('Training', 'Logs') env = gym.make(environment_name) env = DummyVecEnv([lambda: env]) model = PPO('MlpPolicy', env, verbose = 1) model.learn(total_timesteps=10000) PPO_path = os.path.join('Training', 'Saved Models', 'PPO_model') model.save(PPO_path) model = PPO.load(PPO_path, env=env) evaluate_policy(model, env, n_eval_episodes=10, render=True)  I am working on MAC PC with using IDLE.  I installed Pytorch and every other required module.  What may be the cause? 

Answer: You have not installed pygame. The error message already shows that you have to do: pip install gymnasium[classic-control]. Considering the video provided in OG was from 6th of June 2021, the Gym version (not Gymnasium) must have been 0.18.3 or lower. The syntax has changed a lot throughout the newer Gym versions, which causes many errors just like you have experienced. One thing for sure, the video provided does not use Gymnasium. I thus also suggest either to downgrade Gym to a version <= 0.18.3. I could not find out from the video what version they used, but it must be in aforementioned range. Or, you could make yourself familiar with Gymnasium or newer versions of Gym to rewrite parts of the code (since Stable Baselines 3 does work with either version). Might help:  All Gym versions: https://pypi.org/project/gym/#history Gym documentation: https://www.gymlibrary.dev/index.html Gymnasium documentation: https://gymnasium.farama.org/