In this section, we will take a look at the key features that have made the OpenAI Gym toolkit very popular in the reinforcement learning community and led to it becoming widely adopted.

OpenAI Gym provides a simple and common Python interface to environments. Specifically, it takes an action as input and provides observation, reward, done and an optional info object, based on the action as the output at each step. If this does not make perfect sense to you yet, do not worry. We will go over the interface again in a more detailed manner to help you understand. This paragraph is just to give you an overview of the interface to make it clear how simple it is. This provides great flexibility for users as they can design and develop their agent algorithms based on any paradigm they like, and not be constrained to use any particular paradigm because of this simple and convenient interface.

We intuitively feel that we should be able to compare the performance of an agent or an algorithm in a particular task to the performance of another agent or algorithm in the same task. For example, if an agent gets a score of 1,000 on average in the Atari game of Space Invaders, we should be able to tell that this agent is performing worse than an agent that scores 5000 on average in the Space Invaders game in the same amount of training time. But what happens if the scoring system for the game is slightly changed? Or if the environment interface was modified to include additional information about the game states that will provide an advantage to the second agent? This would make the score-to-score comparison unfair, right?

To handle such changes in the environment, OpenAI Gym uses strict versioning for environments. The toolkit guarantees that if there is any change to an environment, it will be accompanied by a different version number. Therefore, if the original version of the Atari Space Invaders game environment was named SpaceInvaders-v0 and there were some changes made to the environment to provide more information about the game states, then the environment's name would be changed to SpaceInvaders-v1. This simple versioning system makes sure we are always comparing performance measured on the exact same environment setup. This way, the results obtained are comparable and reproducible.

All the environments available as part of the Gym toolkit are equipped with a monitor. This monitor logs every time step of the simulation and every reset of the environment. What this means is that the environment automatically keeps track of how our agent is learning and adapting with every step. You can even configure the monitor to automatically record videos of the game while your agent is learning to play. How cool is that?