OK, the only possibility is that you defined a data structure in your global scope called list. That's a very bad idea (and bad practice), since you're forbidding the access to the builtin function, doing so, and there happens the failure. So the problem is on your side.

FYI: in python, the files are merged in a way like this:

preloaded -> most outer scope
    |
    user's solution
        |
        test cases

so what I define in the test cases cannot affect your code, but anything you define in the outer scope (meaning: outside your function) and that isn't declared again in the test cases is left "as is" for the test cases.

Conclusion: do never use name of builtins as variables.

Mmmmh, that's weird. All is fine in the 3 versions in the edit panel, so not related to the new runner...

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Help us help you. Tell us what language.

Sounds like list is used outside of a closure. But only thing I'm sure of is this is not JavaScript or Haskell, so basically I know nothing.

Translator, please fix.