Python Bug: lambda function refers only one environment about tianshou HOT 4 OPEN

You are using a very old version of tianshou. Could you pls try on either 1.0.0 or on the version on master?

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@MischaPanch
I update the python and tianshou version.

1.0.0 0.28.1 2.3.0+cu121 1.24.4 3.11.9 (main, Apr 6 2024, 17:59:24) [GCC 9.4.0] linux

However, this lambda function issue remains.

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Hi @maguro27,

It seems that env is not looked up until the lambda function is called, but by the end of the loop, env is bound to the last element in the list, hence you get the last environment four times. You can read more about it and closures with lambdas here.

This should now work as expected since the default value for env is evaluated when the lambda function is defined:

ts_train_envs = DummyVectorEnv([lambda: env=env for env in train_envs])

Which Tianshou tutorial are you looking at?

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@dantp-ai

Thank you for your comments.
I understand I misunderstood the behavior of the lambda function.

Tianshou tutorials only use default gym environments.
Hence, I misunderstand the behavior.
Therefore, I think maintainers might want to add information for using custom environments (e.g., use the gymnasium register function, then use it. or use "lambda: env=env".).

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