Mypy crashes if there is no 'function' or 'module' in builtins

[vlasovskikh]

You can use types.FunctionType instead of builtins.function. See the original crash in the CI results here python/typeshed#876.

[vlasovskikh]

The same applies to builtins.module and types.ModuleType.

[JukkaL]

The reason mypy has these fake definitions in builtins is to get tidier error messages. We could instead translate types.FunctionType to function when generating messages. module is similar.

[vlasovskikh]

Having function and module in builtins results in false negatives where a type checkers accepts function and module in the user code as built-ins.

[ilevkivskyi]

The module part of this issue is fixed by #3107

[vlasovskikh]

I believe function is no longer an issue as well, since it has been renamed to __function.

[ilevkivskyi]

@vlasovskikh class function: ... is still defined here https://github.com/python/typeshed/blob/master/stdlib/2and3/builtins.pyi#L876, there are some function arguments that has ben renamed to __function few month ago.

So I think this is something still worth fixing. I would prefer to use types.FunctionType as a fallback for functions (or other types classes depending on kind of callable we deal with, like bound method, unbound method, etc.). There is however subtle question of what should be the fallback for user declared Callable, see e.g. a hot discussion in #5958