code: def get_app_submodules(submodule_name):
      
      for name, module in get_app_modules():
          if module_has_submodule(module, submodule_name):
              yield name, import_module('%s.%s' % (name, submodule_name))
docs: From wagtail.utils
      Searches each app module for the specified submodule
      yields tuples of (app_name, module)