code: def _identify(self, dataframe):
          
          idx = ((dataframe[self.channels[0]] <= self.vert[1]) &
                 (dataframe[self.channels[0]] >= self.vert[0]))
  
          if self.region == 'out':
              idx = ~idx
  
          return idx
docs: Return bool series which is True for indexes that 'pass' the gate