cpython/Misc/mypy/README.md

Mypy path symlinks

This directory stores symlinks to standard library modules and packages that are fully type-annotated and ready to be used in type checking of the rest of the stdlib or Tools/ and so on.

Due to most of the standard library being untyped, we prefer not to point mypy directly at Lib/ for type checking. Additionally, mypy as a tool does not support shadowing typing-related standard libraries like types, typing, and collections.abc.

So instead, we set mypy_path to include this directory, which only links modules and packages we know are safe to be type-checked themselves and used as dependencies.

See Lib/_pyrepl/mypy.ini for an example.