code: def prefix(self, sign: Optional[PrefixSign] = None,
                 symbol: bool = False) -> str:
          
          prefixes = SI_PREFIXES_SYM if \
              symbol else SI_PREFIXES
  
          key = self._validate_enum(item=sign, enum=PrefixSign)
          return self.random.choice(prefixes[key])
docs: Get a random prefix for the International System of Units.
  
          :param sign: Sing of number.
          :param symbol: Return symbol of prefix.
          :return: Prefix for SI.
          :raises NonEnumerableError: if sign is not supported.
  
          :Example:
              mega