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Fix Python Shared-State Bugs: Mutable Defaults, Shallow Copies and Dataclass field(default_factory)

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Self-Hosting & Infra beginner 6 min read $0.01 Updated 2026-10-20

Explains Python aliasing bugs: mutable default arguments, dataclass mutable default ValueError, class attributes shared across instances, list multiplication, shallow copy versus deepcopy, defensive copies and immutable alternatives.

Instances share the same list, a copied dict changes the original, or a function remembers old arguments. Understand mutable defaults, shallow versus deep copy and use default_factory.

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#python#dataclasses#mutable-default#copy#debugging

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