OpenAI Gym - AttributeError：模块“contextlib”没有属性“nullcontext”

Question

当我尝试从 docker google 计算引擎上的 docker 容器运行命令时，我遇到了此错误。

这是堆栈跟踪：

Traceback (most recent call last):
  File "train.py", line 16, in <module>
    from stable_baselines.ppo1 import PPO1
  File "/home/selfplay/.local/lib/python3.6/site-packages/stable_baselines/__init__.py", line 3, in <module>
    from stable_baselines.a2c import A2C
  File "/home/selfplay/.local/lib/python3.6/site-packages/stable_baselines/a2c/__init__.py", line 1, in <module>
    from stable_baselines.a2c.a2c import A2C
  File "/home/selfplay/.local/lib/python3.6/site-packages/stable_baselines/a2c/a2c.py", line 3, in <module>
    import gym
  File "/home/selfplay/.local/lib/python3.6/site-packages/gym/__init__.py", line 13, in <module>
    from gym.envs import make, spec, register
  File "/home/selfplay/.local/lib/python3.6/site-packages/gym/envs/__init__.py", line 10, in <module>
    _load_env_plugins()
  File "/home/selfplay/.local/lib/python3.6/site-packages/gym/envs/registration.py", line 269, in load_env_plugins
    context = contextlib.nullcontext()
AttributeError: module 'contextlib' has no attribute 'nullcontext'

Answer 1

这似乎是 python 3.6 和gym 的问题。将我的容器升级到 python 3.7 解决了这个问题。

Answer 2

降级gym的版本也可能解决这个问题。我在 python 3.6 中也遇到了这个错误。我将gym的版本从0.21.0降级到0.15.7，然后就修复了。