The modulefinder module (Lib/modulefinder.py) provides a ModuleFinder class (plus 2 helpers) you can use to see what modules a script imports (directly or indirectly).  The module's implementation is centered on the old imp.find_/load_module() API (which has been deprecated).  The implementation should be refactored to reflect/make use of the newer import-related APIs.

The documented API for ModuleFinder is very small.  However, it has quite a few methods that are "public" in the sense that their names do not start with an underscore.  This will make any kind of refactoring trickier.