gh-144812: ✨ Add public argparse group typing protocols#150597
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gh-144812: ✨ Add public argparse group typing protocols#150597gaborbernat wants to merge 1 commit into
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ArgumentParser.add_argument_group() and add_mutually_exclusive_group() return objects whose only public name was the private _ArgumentGroup and _MutuallyExclusiveGroup. Code that stores or passes these objects had no public type to annotate against, forcing callers to reference the underscore-prefixed implementation classes. Expose them as structural protocols rather than aliasing the concrete classes, so the implementation stays private and free to evolve while callers get a stable contract to annotate against. The protocols are built on first attribute access through the module __getattr__, keeping typing off the import path: argparse sits on the start-up path of most CLIs and does not otherwise import typing.
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ArgumentParser.add_argument_group()andadd_mutually_exclusive_group()return objects whose only name is the private_ArgumentGroupand_MutuallyExclusiveGroup. Code that stores or passes these objects around has no public type to annotate against, so callers reach for the underscore-prefixed implementation classes. A GitHub code search turns up roughly 140 projects doing exactly that. 📦This exposes two public names,
argparse.ArgumentGroupandargparse.MutuallyExclusiveGroup, as structuraltyping.Protocols that guarantee theadd_argument()method callers rely on. Modelling them as protocols rather than aliasing the concrete classes keeps the implementation private and free to evolve, which addresses the concern raised on the issue that typing needs should not turn inner classes into frozen public API. ✨ The protocols are built on first attribute access through the module__getattr__, soimport argparsestays off thetypingimport path — relevant becauseargparsesits on the start-up path of most CLIs and does not otherwise importtyping.Type checkers read typeshed rather than
Lib/argparse.py, so these names take effect for end users oncestdlib/argparse.pyideclares the protocols and points the two return types at them. I confirmed that change makes mypy, pyright, ty, and pyrefly all resolve the public names; a matchingpython/typeshedPR will follow.