code: def wheelEvent(self, ev, axis=None):
          
          state = None
          # ctrl reverses mouse operation axis
          if ev.modifiers() == QtCore.Qt.ControlModifier:
              state = self.mouseEnabled()
              self.setMouseEnabled(not state[0], not state[1])
          if self._zeroWheel:
              ev.pos = lambda : self.mapViewToScene(QtCore.QPoint(0,0))
          super(SpikeyViewBox, self).wheelEvent(ev, axis)
          if state is not None:
              self.setMouseEnabled(*state)
docs: Reacts to mouse wheel movement, custom behaviour switches zoom
          axis when ctrl is pressed, and sets the locus of zoom, if zeroWheel
          is set.