Python中的循环出错

Question

我有列表lst = [1, 2, 3, 4, 5, 6, 3, 5, 3]和每个迭代，其中elem == 3我想打印字符串之前，而elem不是3再次。 我想

2 3: 
0 1 
1 2 
6 3: 
3 4 
4 5 
5 6 
8 3: 
7 5 

但我不知道，怎么去以前的字符串

for i, el in enumerate(lst): 
    if lst[i] == 3: 
     print i, el 
     i -= 1 

但它精心elem-1

Answer 1

像这样的事情？

lst = [1, 2, 3, 4, 5, 6, 3, 5, 3] 
    previous = [] 

    for i, el in enumerate(lst): 
     if lst[i] == 3: 
      print i, el,":" 
      for p in previous: 
       print p[0] , p[1] 
      previous = [] 
     else: 
      previous.append((i,el)) 

Answer 2

您可以尝试使用片实施为：？

lst = [1, 2, 3, 4, 5, 6, 3, 5, 3] 

start_pos = 0 
for idx, val in enumerate(lst): 
    if val == 3: 
     print idx,val,":" 
     for p_idx, p_val in enumerate(lst[start_pos:idx]): 
      print p_idx+start_pos,p_val 
     start_pos = idx+1