code: def _module_parents(module_name):
          '''
          >>> list(Register._module_parents('a.b'))
          ['a.b', 'a', '']
          '''
          spl = module_name.split('.')
          for i in range(len(spl), 0, -1):
              yield '.'.join(spl[0:i])
          if module_name:
              yield 'f _module_parents(module_name):
          '''
          >>> list(Register._module_parents('a.b'))
          ['a.b', 'a', '']
          '''
          spl = module_name.split('.')
          for i in range(len(spl), 0, -1):
              yield '.'.join(spl[0:i])
          if module_name:
              yield ''
docs: >>> list(Register._module_parents('a.b'))
          ['a.b', 'a', '']