evn.render() in doc examples don't run unless n_envs=1 in make_vec_env()

This is possibly quite trivial, but the evn.render() lines of the code examples do not run for multiprocess environments unless unless n_envs=1 in make_vec_env().

For example, the code example on this page

• https://stable-baselines.readthedocs.io/en/master/modules/ppo2.html

I’m using stable-baselines 2.10.0.

The error is

Traceback (most recent call last):
  File "<stdin>", line 4, in <module>
  File "/lib/python3.6/site-packages/stable_baselines/common/vec_env/dummy_vec_env.py", line 85, in render
    return super().render(*args, **kwargs)
TypeError: render() missing 1 required positional argument: 'mode'

[araffin]

@Miffyli what version are you using?

The following code works for me (using latest master version):

from stable_baselines.common.cmd_util import make_vec_env

n_envs = 4
env = make_vec_env('CartPole-v1', n_envs=n_envs)
 
obs = env.reset()
for _ in range(100):
    env.step([env.action_space.sample() for _ in range(n_envs)])
    env.render()

(it works also with SB3)

[pstansell]

Thanks for the amazingly quick resolution!