Grid2Op: Garbage collection bug for forecast observation

Environment

• Grid2op version: 1.9.7
• System: Springdale Open Enterprise Linux 9.2 (Parma)

Bug description

Appending an Observation object returned from forecast_obs = obs.forecast_env().reset() to a list class attribute in a function results in forecast_obs being garbage collected when we the function is exited. I believe that this is due to the fact that __del__ is being called on forecast_obs._obs_env when the function foo below is exited.

The error still persists if we remove LightSimBackend (i.e. use the default backend) or change the environment or if we copy forecast_obs before adding it to the list.

How to reproduce

Command line

Code snippet

import grid2op
from lightsim2grid import LightSimBackend

env_name = "l2rpn_wcci_2022"
env = grid2op.make(env_name, backend=LightSimBackend())
_ = env.reset()

class Manager:
    obs_list = []

def foo():
    obs = env.reset()
    forecast_env = obs.get_forecast_env()
    forecast_obs = forecast_env.reset()
    Manager.obs_list.append(forecast_obs)
    print(f"forecast_obs: {forecast_obs}")
    print(f"[FOO] Manager.obs_list[0]._obs_env: {Manager.obs_list[0]._obs_env}")
    print(f"[FOO] Manager.obs_list[0]._obs_env.backend is None: {Manager.obs_list[0]._obs_env.backend is None}")


if __name__ == '__main__':
    foo()
    print(f"Manager.obs_list[0]._obs_env: {Manager.obs_list[0]._obs_env}")
    print(f"Manager.obs_list[0]._obs_env.backend is None: {Manager.obs_list[0]._obs_env.backend is None}")

Current output

forecast_obs: <grid2op.Space.GridObjects.ObservationWCCI2022_l2rpn_wcci_2022 object at 0x7f2f7e5f3e80>    
[FOO] Manager.obs_list[0]._obs_env: <grid2op.Environment._obsEnv._ObsEnv_l2rpn_wcci_2022 object at 0x7f2f7e
5f3ee0>                                                                                                   
[FOO] Manager.obs_list[0]._obs_env.backend is None: False                                                  
Manager.obs_list[0]._obs_env: <grid2op.Environment._obsEnv._ObsEnv_l2rpn_wcci_2022 object at 0x7f2f7e5f3ee0
>                                                                                                          
Manager.obs_list[0]._obs_env.backend is None: True 

Expected output

Manager.obs_list[0]._obs_env.backend is None: False

The backend should still remain even after we exit foo