Handle common cases of mutable default arguments explicitly #2651
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Why are the changes needed?
In #2401 we added a check against mutable default arguments where we simply confirmed that the object was hashable. This works, but it's too restrictive as it prevents other commonly used objects (e.g. dataclasses) from being used as default values.
Even sophisticated linters like ruff only detect mutable default arguments for lists, dictionaries, and sets. For example, this sample code:
returns this error in ruff:
Notice how the dataclass is not classified as a mutable default arg.
What changes were proposed in this pull request?
We handle the 3 common cases explicitly instead of checking if the object is hashable.
How was this patch tested?
unit tests.
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