Box2D dependency fails on Linux

[christopherhesse]

The Box2D library used by setup.py doesn't seem to work, and also the tests do not seem to catch this.

Steps to reproduce:

apt-get update
apt-get install swig
pip install gym[box2d]
python -c "import Box2D"

  File "<string>", line 1, in <module>
  File "/opt/conda/lib/python3.6/site-packages/Box2D/__init__.py", line 20, in <module>
    from .Box2D import *
  File "/opt/conda/lib/python3.6/site-packages/Box2D/Box2D.py", line 434, in <module>
    RAND_LIMIT = _Box2D.RAND_LIMIT
AttributeError: module 'Box2D._Box2D' has no attribute 'RAND_LIMIT'

@pzhokhov has suggested that box2d-py is in fact the correct dependency to put in setup.py and not box2d-kengz but that may require testing on mac and linux.

[DuaneNielsen]

I could only get it working on mac with box2d-kengz box2d didn't work for me...

[christopherhesse]

@pzhokhov I tried box2d-py on my mac and it failed, it seems like box2d-kengz is required on mac while box2d-py is required on linux. Is there some way to make this work correctly on both platforms?

[christopherhesse]

This also implies we have no mac tests for these environments, is that the case?

[christopherhesse]

Since there is no valid configuration of box2d packages, could we get a note in the readme or something as a workaround until we have a box2d package that works? @pzhokhov

[BStudent]

box2d doesn't seem to work currently for Pop!_OS (System76' GPU-friendly unbuntu derivative), however box2d-kengz does.

[pzhokhov]

added a note to README:
#1120

[christopherhesse]

This was fixed by #1120