code: def is_package(self, fullname):
          
          filename = os.path.split(self.get_filename(fullname))[1]
          filename_base = filename.rsplit('.', 1)[0]
          tail_name = fullname.rpartition('.')[2]
          return filename_base == '__init__' and tail_name != '__init__'
docs: Concrete implementation of InspectLoader.is_package by checking if
          the path returned by get_filename has a filename of '__init__.py'.