def pmt_angles(self):
        """A list of PMT directions sorted by PMT channel, on DU-1, floor-1"""
        if self._pmt_angles == []:
            mask = (self.pmts.du == 1) & (self.pmts.floor == 1)
            self._pmt_angles = self.pmts.dir[mask]
        return self._pmt_angles
def pmt_angles ( self ) : if self . _pmt_angles == [ ] : mask = ( self . pmts . du == 1 ) & ( self . pmts . floor == 1 ) self . _pmt_angles = self . pmts . dir [ mask ] return self . _pmt_angles
A list of PMT directions sorted by PMT channel, on DU-1, floor-1