code: def update_desc_lsib_path(desc):
      '''
          leftSibling
          previousSibling
          leftSib
          prevSib
          lsib
          psib
          
          have the same parent,and on the left
      '''
      if(desc['sib_seq']>0):
          lsib_path = copy.deepcopy(desc['path'])
          lsib_path[-1] = desc['sib_seq']-1
          desc['lsib_path'] = lsib_path
      else:
          pass
      return(descf update_desc_lsib_path(desc):
      '''
          leftSibling
          previousSibling
          leftSib
          prevSib
          lsib
          psib
          
          have the same parent,and on the left
      '''
      if(desc['sib_seq']>0):
          lsib_path = copy.deepcopy(desc['path'])
          lsib_path[-1] = desc['sib_seq']-1
          desc['lsib_path'] = lsib_path
      else:
          pass
      return(desc)
docs: leftSibling
          previousSibling
          leftSib
          prevSib
          lsib
          psib
          
          have the same parent,and on the left