list[str] vs List[str] from typing

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Before Python 3.9, built-in collection types like list, dict, and tuple could not be subscripted at runtime. Writing 'list[str]' in a function annotation would raise TypeError on Python 3.8. The typing module introduced List, Dict, Tuple, etc. as generic aliases that could be subscripted on older versions. Python 3.9 (PEP 585) made the built-ins themselves subscriptable, so list[str] and List[str] are now semantically identical. The modern convention is to drop the typing imports and use lowercase built-in generics. For code that must run on 3.8, either use List from typing or add 'from __future__ import annotations' to defer annotation evaluation. Many data science codebases are pinned to 3.9+ now, so you will see both styles in the wild.