code: def initPos(self, startpos=0.0):
          
          spos = startpos
          for ele in self._lattice_eleobjlist:
              # print("{name:<10s}: {pos:<10.3f}".format(name=ele.name, pos=spos))
              ele.setPosition(spos)
              spos += ele.getLength()
docs: initialize the elements position [m] in lattice, the starting
              point is 0 [m] for the first element by default.
  
              :param startpos: starting point, 0 [m] by default