code: def unicode_is_ascii(u_string):
      
      assert isinstance(u_string, str)
      try:
          u_string.encode('ascii')
          return True
      except UnicodeEncodeError:
          return False
docs: Determine if unicode string only contains ASCII characters.
  
      :param str u_string: unicode string to check. Must be unicode
          and not Python 2 `str`.
      :rtype: bool