Shadows built-in names “function” and “module” with PyCharm

function is "defined" in builtins.pyi:

class function:
    # TODO not defined in builtins!   
    __name__ = ...  # type: str
    __qualname__ = ...  # type: str
    __module__ = ...  # type: str
    __code__ = ...  # type: Any
    __annotations__ = ...  # type: Dict[str, Any] 

Keep in mind I used "defined" vs defined. Check out this absurdity:

foo = function

raises

Traceback (most recent call last):
  File "main.py", line 117, in <module>
    foo = function
NameError: name 'function' is not defined

Yet if you do function = 'a' the IDE will complain (as you noticed) that this shadows a built-in name (even though function is clearly not actually defined).

The exact behavior repeats with module.

This is because (as far as I understand, anyone please correct me if I'm wrong) pyi files are only there to provide type hints (as PEP-484 suggests).

So, I'm not sure if this warning is a bug in Pycharm's linter (perhaps it should not be looking at "definitions" in .pyi files) or an intended behavior.

Either way, module and function are probably not good variable names anyway.

Per PY-8672, since March 2014 there is an ability to ignore certain names with this inspection. Open Settings, search "Shadowing built-ins", click on the inspection name, and use the Options section to add names the inspection should whitelist.