How to create new environments for Gym

Create a new repo called gym-foo, which should also be a PIP package.
A good example is https://github.com/openai/gym-soccer.

It should have at least the following files:

gym-foo/
  README.md
  setup.py
  gym_foo/
    __init__.py
    envs/
      __init__.py
      foo_env.py
      foo_extrahard_env.py

gym-foo/setup.py should have:

from setuptools import setup

setup(name='gym_foo',
      version='0.0.1',
      install_requires=['gym']  # And any other dependencies foo needs
)

gym-foo/gym_foo/__init__.py should have:

from gym.envs.registration import register

register(
    id='foo-v0',
    entry_point='gym_foo.envs:FooEnv',
)
register(
    id='foo-extrahard-v0',
    entry_point='gym_foo.envs:FooExtraHardEnv',
)

gym-foo/gym_foo/envs/__init__.py should have:

from gym_foo.envs.foo_env import FooEnv
from gym_foo.envs.foo_extrahard_env import FooExtraHardEnv

gym-foo/gym_foo/envs/foo_env.py should look something like:

import gym
from gym import error, spaces, utils
from gym.utils import seeding

class FooEnv(gym.Env):
  metadata = {'render.modes': ['human']}

  def __init__(self):
    ...
  def step(self, action):
    ...
  def reset(self):
    ...
  def render(self, mode='human'):
    ...
  def close(self):
    ...

After you have installed your package with pip install -e gym-foo, you can create an instance of the environment with gym.make('gym_foo:foo-v0')