comefrom: <doocs>2074.Reverse Nodes in Even Length Groups_1.py
code: def reverse(head, l):
      prev, cur, tail = None, head, head
      i = 0
      while cur and i < l:
          t = cur.next
          cur.next = prev
          prev = cur
          cur = t
          i += 1
      tail.next = cur
      return prev
masked: def sample_funcname ( var_0 , var_1 ) :
      var_3 , var_4 , var_5 = None , var_0 , var_0
      var_7 = 0
      while var_4 and var_7 < var_1 :
          var_9 = var_4.next
          var_4.next = var_3
          var_3 = var_4
          var_4 = var_9
          var_7 += 1
      var_5.next = var_4
      return var_3
  