[Enhancement] Deprecate --gym-packages argument

[ernestum]

🚀 Feature

Deprecate or even remove the --gym-packages argument.

Motivation

Since gym 0.21.0 you can pass <package>:<gym_id> to gym.make() to make it automatically import the given package. This turns the --gym-packages flag into duplicate functionality that unnecessarily clutters the interface.

Pitch

Remove the argument and add a hint about the feature in the documentation.

Alternatives

No response

Additional context

I learned about this feature by @RedTachyon here

Checklist

• I have checked that there is no similar issue in the repo

[araffin]

Since gym 0.21.0 you can pass :<gym_id> to gym.make() to make it automatically import the given package.

Interesting... I didn't know about that undocumented feature. Yes, makes sense then (and we need to double check but the yaml/python config file should work too with this). The other thing we need to double check is the name convention for the envs.

[RedTachyon]

To explain in some more detail how it works: if you do gym.make("module_name:envid-v0"), then internally it gets split on the colon into module_name and envid-v0. Internally then it calls importlib.import_module("module_name"), i.e. roughly the same as import package_name

If this module registers some environments upon being imported, then those environments are then in scope and are created with the usual gym.make("envid-v0")

FWIW the feature is documented in Gymnasium, but maybe not as exposed as it should be

[araffin]

To explain in some more detail how it works: if you do gym.make("module_name:envid-v0"), then internally it gets split on the colon into module_name and envid-v0. Internally then it calls importlib.import_module("module_name")

yes, that's what --gym-packages is doing too.

After a quick check, gym.make("module:env-id") works but not gym.spec("module:env-id"), we need to see if we still need that.

rl-baselines3-zoo/rl_zoo3/exp_manager.py

Lines 608 to 612 in 660f2d3

	# Define make_env here so it works with subprocesses
	# when the registry was modified with `--gym-packages`
	# See https://github.com/HumanCompatibleAI/imitation/pull/160
	try:
	spec = gym.spec(self.env_name.gym_id)

[araffin]

We will also have another problem:

rl-baselines3-zoo/rl_zoo3/train.py

Lines 161 to 171 in 660f2d3

	registered_envs = set(gym.envs.registry.keys()) # pytype: disable=module-attr
	# Add gym 0.26 envs
	registered_envs.update(gym26.envs.registry.keys()) # pytype: disable=module-attr
	# If the environment is not found, suggest the closest match
	if env_id not in registered_envs:
	try:
	closest_match = difflib.get_close_matches(env_id, registered_envs, n=1)[0]
	except IndexError:
	closest_match = "'no close match found...'"
	raise ValueError(f"{env_id} not found in gym registry, you maybe meant {closest_match}?")

EDIT: we can skip that check when module:env-id is passed.

[ernestum]

BTW: environment name normalization for gym_ids with this prefix should be fixed soonish: huggingface/huggingface_sb3#32