code: def _sumImages(self,numarrayObjectList):
          
          if numarrayObjectList in [None, []]:
              return None
  
          tsum = np.zeros(numarrayObjectList[0].shape, dtype=numarrayObjectList[0].dtype)
  
          for image in numarrayObjectList:
              tsum += image
  
          return tsum
docs: Sum a list of numarray objects.