python - 删除和添加项目到迭代列表

Question

我正在迭代两个列表，如下所示:

list1 = [z]
list2 = [z-t,z-s,s-a,a-n, g-z]
for e in list1:
 for t in list2:
  # if item from list2 contains item from list1 (before "-")
  # remove the item from list2 and append part after "-" to list1
  # iterate again until no change is made or list2 is empty

我无法解决的问题是，当我从 list2 中删除该项目时，它会转到下一个项目，而我无法阻止它。例如

list2 = [z-t,z-s,s-a....]
          ^ removing this while iterating
next iteration jumps over one item
list2 = [z-s, s-a,...]
               ^ this is where I am second iteration
list2 = [z-s, s-a,...]
          ^ this is where I want to be

有什么办法可以做到这一点吗？

Answer 1

有几种方法可以实现这一点，其中一种是向后迭代列表，即

for e in list1:
    for t in list2[::-1]:  # This iterates over the list backwards
        # Do your check
        # Remove the element

如果你需要向前处理它，你可以迭代一个副本，这样你就可以在迭代初始内容的同时改变原始列表，即

for e in list1:
    for t in list2[:]:  # The [:] syntax feeds you your data via a new list.
        # Do your check
        # Remove the element, and not worry about mutating the original list length