> The documentation should state that "pathname" will be None (not the empty string) for built-in and frozen modules in order to be in line with the implementation.

Both the "file" and "pathname" will be None for built-in and frozen modules, right? In the PR @ericsnowcurrently suggested add:

>  If the module is built-in or frozen then *file* and *pathname* are both ``None`` and the *description* tuple contains empty...

I think it also works.