code: def _get_params(self, validator_parameter, name_prefix):
      
      params_validator = self.request.get(validator_parameter)
  
      user_params = {}
      for key in self.request.arguments():
        if key.startswith(name_prefix):
          values = self.request.get_all(key)
          adjusted_key = key[len(name_prefix):]
          if len(values) == 1:
            user_params[adjusted_key] = values[0]
          else:
            user_params[adjusted_key] = values
  
      if params_validator:
        resolved_validator = util.for_name(params_validator)
        resolved_validator(user_params)
  
      return user_params
docs: Retrieves additional user-supplied params for the job and validates them.
  
      Args:
        validator_parameter: name of the request parameter which supplies
          validator for this parameter set.
        name_prefix: common prefix for all parameter names in the request.
  
      Raises:
        Any exception raised by the 'params_validator' request parameter if
        the params fail to validate.
  
      Returns:
        The user parameters.