There's more...

You may wonder why we need to install Atari dependencies. In fact, there are a few more environments that do not accompany the installation of gym, such as Box2d, Classic control, MuJoCo, and Robotics.

Take the Box2d environments, for example; we need to install the Box2d dependencies before we first run the environments. Again, two installation approaches are as follows:

pip install gym[box2d]
pip install -e '.[box2d]'

After that, we can play around with the LunarLander environment, as follows:

>>> env = gym.make('LunarLander-v2')
>>> env.reset()
array([-5.0468446e-04,  1.4135642e+00, -5.1140346e-02,  1.1751971e-01,
       5.9164839e-04,  1.1584054e-02, 0.0000000e+00,  0.0000000e+00],
     dtype=float32)
>>> env.render()

A game window will pop up: