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Yep, a renowned Python footgun. Although Lambda container reuse adds a modern twist to it.

Can I ask what editor you were using? Because decent ones should have warned you about mutable default args.

Shout out to the amazing Pyright, the fast and feature-complete python LSP that you can use with any editor that supports the LSP protocol!

I'm using VSCode with different Python specific extensions, like Pylance which uses Pyright, but it didn't warn me about the mutable function parameter. RIP

Huh, that sucks. I use Intellij Ultimate for pretty much everything, and it (and the Python focused Pycharm) will definitely warn on this particular Python quirk.

You're right, I checked, and pyright only warns about function calls in default arguments, not mutable containers.

I started a discussion in Pyright's repo here[0].

[0] https://github.com/microsoft/pyright/discussions/2306

Thanks to the maintainer's great responsiveness, Pyright will implement such a warning soon: https://github.com/microsoft/pyright/issues/2308

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