Getting ImportError with GL library when trying to render CartPole environment

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1

I’m working with OpenAI Gym in a Colab environment and trying to run a basic CartPole simulation. Here’s my code:

import gym
env = gym.make('CartPole-v1')
env.reset()
for i in range(500):
    env.render()
    action = env.action_space.sample()
    env.step(action)

The code runs but I’m getting this warning message:

WARN: gym.spaces.Box autodetected dtype as <class 'numpy.float32'>. Please provide explicit dtype.

More importantly, when it hits the render() method, I get an error about missing GL library:

Error occured while running `from pyglet.gl import *`
The original exception was:
ImportError: Library "GL" not found.

I already tried installing PyOpenGL using pip but that didn’t solve the issue. What’s the correct way to handle rendering in Colab notebooks? Are there alternative libraries I should install instead?

2

I encountered the same problem while working with Gym in Colab. Due to Colab’s lack of OpenGL libraries, the render method can fail. To resolve this issue, you can install the necessary system dependencies by running the following commands: !apt-get update, !apt-get install -y xvfb python-opengl ffmpeg, and then !pip install pyvirtualdisplay. After that, initialize a virtual display by adding from pyvirtualdisplay import Display, followed by display = Display(visible=0, size=(400, 300)) and display.start(). This setup allows the rendering to work properly, leveraging the libraries provided by xvfb.

3

The virtual display approach works, but here’s a simpler fix I’ve been using. Skip the OpenGL headaches and just capture frames as arrays, then display them with matplotlib. Before your loop, add frames = []. Inside the loop, use frames.append(env.render(mode='rgb_array')) instead of env.render(). After the loop, visualize everything with matplotlib’s imshow. This completely sidesteps the GL library mess and you still see what’s happening. It’s not real-time, but it’s perfect for debugging and analysis.

4

colab doesn’t really support opengl rendering directly. u can switch to env.render(mode='rgb_array') for pixel data without the extra libraries. just use matplotlib for displaying the frames or savin’em as images.