code: def generate(self):
          
          try:
              model = self.schema().model()
          except AttributeError:
              return os.urandom(self.__bits).encode('hex')
          else:
              while True:
                  token = os.urandom(self.__bits).encode('hex')
                  if model.select(where=orb.Query(self) == token).count() == 0:
                      return token
docs: Generates a new token for this column based on its bit length.  This method
          will not ensure uniqueness in the model itself, that should be checked against
          the model records in the database first.
  
          :return:    <str>