python - 这个 Python 简写有什么作用？ {s[ :i] + s[i+1:] for s in level for i in range(len(s))}

Question

level = {s[:i] + s[i+1:] for s in level for i in range(len(s))}

我以为和这个一样，其实不是这样

for s in level:
  for i in range(len(s)):
    level = {s[:i] + s[i+1:]}

来源:https://leetcode.com/problems/remove-invalid-parentheses/discuss/75028/Short-Python-BFS

Answer 1

它在功能上等同于:

new_level = set()
for s in level:
    for i in range(len(s)):
        new_level.add(s[:i] + s[i+1:])
level = new_level