title: OpenAI Gym - AttributeError: module 'contextlib' has no attribute 'nullcontext'
body: <p>I'm running into this error when trying to run a command from docker a docker container on google compute engine.</p>
  <p>Here's the stacktrace:</p>
  <pre><code>Traceback (most recent call last):
    File &quot;train.py&quot;, line 16, in &lt;module&gt;
      from stable_baselines.ppo1 import PPO1
    File &quot;/home/selfplay/.local/lib/python3.6/site-packages/stable_baselines/__init__.py&quot;, line 3, in &lt;module&gt;
      from stable_baselines.a2c import A2C
    File &quot;/home/selfplay/.local/lib/python3.6/site-packages/stable_baselines/a2c/__init__.py&quot;, line 1, in &lt;module&gt;
      from stable_baselines.a2c.a2c import A2C
    File &quot;/home/selfplay/.local/lib/python3.6/site-packages/stable_baselines/a2c/a2c.py&quot;, line 3, in &lt;module&gt;
      import gym
    File &quot;/home/selfplay/.local/lib/python3.6/site-packages/gym/__init__.py&quot;, line 13, in &lt;module&gt;
      from gym.envs import make, spec, register
    File &quot;/home/selfplay/.local/lib/python3.6/site-packages/gym/envs/__init__.py&quot;, line 10, in &lt;module&gt;
      _load_env_plugins()
    File &quot;/home/selfplay/.local/lib/python3.6/site-packages/gym/envs/registration.py&quot;, line 269, in load_env_plugins
      context = contextlib.nullcontext()
  AttributeError: module 'contextlib' has no attribute 'nullcontext'
  </code></pre>