code: def get_threshold(self):
          
  
          if self.threshold.startswith('+'):
              if self.threshold[1:].isdigit():
                  self._threshold = int(self.threshold[1:])
                  self._upper = True
          elif self.threshold.startswith('-'):
              if self.threshold[1:].isdigit():
                  self._threshold = int(self.threshold[1:])
                  self._upper = False
          else:
              if self.threshold.isdigit():
                  self._threshold = int(self.threshold)
                  self._upper = True
          if not hasattr(self, '_threshold'):
              raise ValueError('Invalid threshold')
docs: Get and validate raw RMS value from threshold