code: def _walk_modules(modules, class_name, path, ignored_formats, args):
      
      for module in _iter_modules(modules=modules,
                                  class_name=class_name,
                                  path=path,
                                  ignored_formats=ignored_formats,
                                  args=args):
          for section in module.sections:
              for lecture in section.lectures:
                  for resource in lecture.resources:
                      yield module, section, lecture, resource
docs: Helper generator that traverses modules in returns a flattened
      iterator.