code: def _select_in_voltage_range(self, min_voltage=None, max_voltage=None):
          
          min_voltage = min_voltage if min_voltage is not None \
              else self.min_voltage
          max_voltage = max_voltage if max_voltage is not None \
              else self.max_voltage
          return list(filter(lambda p: min_voltage <= p.voltage <= max_voltage,
                             self.voltage_pairs))
docs: Selects VoltagePairs within a certain voltage range.
  
          Args:
              min_voltage (float): The minimum allowable voltage for a given
                  step.
              max_voltage (float): The maximum allowable voltage allowable for a
                  given step.
  
          Returns:
              A list of VoltagePair objects