Check Action Type

[MentalGear]

https://github.com/hill-a/stable-baselines/issues/707

Description

TypeError: 'int' object is not subscriptable Ran a couple time into this bug, and found it really hard to debug within stable baselines. To spare others (as well as my future self) much frustration I would suggest to add a type check to wrapper envs like dummyEnv (or only check_env?) before using the action to make sure it's an iterable, before continuing with the code.

The following assertion will give a developer friendly error message that's easy to understand and offers an immediate solution, saving much frustration.

Motivation and Context

https://github.com/hill-a/stable-baselines/issues/707

• [x] I have raised an issue to propose this change

closes #707

Types of changes

• [x] New feature (non-breaking change which adds functionality)

Checklist:

• [x] I've read the CONTRIBUTION guide (required)
• [x] I have updated the changelog accordingly (required).
• [ ] My change requires a change to the documentation.
• [x] I have updated the tests accordingly (required for a bug fix or a new feature).
• [ ] I have updated the documentation accordingly.
• [ ] I have ensured pytest and pytype both pass (by running make pytest and make type).

[araffin]

Hello, thanks for the PR, please don't forget to add a test, and add your username to the changelog. note that some tests are failing because of an internal wrapper (unvecwrapper).

[MentalGear]

OK, added tests. I'm not sure though if it's the right approach to check each step of the base env if the action type received is compatible, as it seems a bit of unnecessary overhead. Maybe just check on the first run ?