How to Fix Common Gymnasium Setup Problems

Old tutorials use gym

One of the first things you’ll run into is code that says:

import gym

while your installation uses:

import gymnasium as gym

Gymnasium is the maintained fork of OpenAI Gym, and its API differs from older Gym releases. In particular, modern Gymnasium uses terminated and truncated instead of the old single done value. citeturn0search2turn0search10

If you’re following an old tutorial, don’t blindly downgrade everything to make it work. Check the Gymnasium migration guide first. citeturn0search10

An environment cannot be found

If gym.make() complains that an environment is not registered, check the environment name and whether its optional dependency is installed.

Gymnasium separates many environment families into optional dependencies. You don’t need every extra installed for the basic environments.

For example, Box2D environments have their own installation requirements. citeturn0search0

Box2D installation errors

Box2D is a particularly common source of installation problems because it has native components.

For current Gymnasium releases, the basic installation documented for Box2D is:

pip install swig
pip install "gymnasium[box2d]"

SWIG is required when Box2D needs to be built from source. This is especially relevant on newer Python versions where a compatible pre-built wheel may not be available. citeturn0search0

Gymnasium’s current release notes also note that pygame-ce replaced the older pygame dependency in v1.3.0, including Python 3.14 compatibility work. citeturn0search5

Rendering errors

A basic environment can work perfectly while rendering fails. That’s because rendering often requires additional packages that aren’t necessary for simply stepping through an environment.

If you see an error involving Pygame, install the appropriate Gymnasium extra for the environment family you’re using.

For example, classic-control rendering is one case where the rendering dependency is separate from the core Gymnasium installation. citeturn0search18

done is not working

If you copied an old RL tutorial, you may have code like:

observation, reward, done, info = env.step(action)

Modern Gymnasium returns:

observation, reward, terminated, truncated, info = env.step(action)

The usual episode-ending check is:

if terminated or truncated:
    observation, info = env.reset()

This is an API difference rather than an installation problem. The distinction exists because an environment reaching its terminal state is different from an episode being stopped by a time limit. citeturn0search10

Python version problems

If a package fails to install, check your Python version before changing random dependencies.

This matters particularly for environments with native dependencies. For example, Gymnasium’s current Box2D documentation specifically calls out Python 3.14 and newer versions because the available Box2D wheels differ by Python version. citeturn0search0

Check your version with:

python --version

Then check the installation requirements for the specific environment you are trying to use.

You’re mixing environments

A surprisingly common problem is installing Gymnasium into one Python environment and running the script with another.

Check which Python you’re actually using:

python -c "import sys; print(sys.executable)"

Then check Gymnasium itself:

python -c "import gymnasium; print(gymnasium.__version__)"

If those commands work in your terminal but not in your IDE, the IDE may be using a different interpreter.

The important distinction

When Gymnasium isn’t working, first figure out which layer is actually broken:

Python environment
       ↓
Gymnasium installation
       ↓
Environment package / extra
       ↓
Rendering or native dependency
       ↓
Your RL code

That usually gets you to the problem much faster than reinstalling everything.

For the initial installation and a basic working example, see How to Set Up OpenAI Gymnasium.