如何打破多个循环?

2022-01-29 00:00:00 python break nested-loops control-flow

问题描述

鉴于以下代码(不起作用):

Given the following code (that doesn't work):

while True:
    #snip: print out current state
    while True:
        ok = get_input("Is this ok? (y/n)")
        if ok.lower() == "y": break 2 #this doesn't work :(
        if ok.lower() == "n": break
    #do more processing with menus and stuff

有没有办法让它工作?或者我是否必须先进行一次检查以跳出输入循环，然后再进行一次更有限的检查，以在用户满意的情况下一起跳出外部循环?

Is there a way to make this work? Or do I have do one check to break out of the input loop, then another, more limited, check in the outside loop to break out all together if the user is satisfied?

解决方案

这是另一种简短的方法.缺点是你只能打破外循环，但有时它正是你想要的.

Here's another approach that is short. The disadvantage is that you can only break the outer loop, but sometimes it's exactly what you want.

for a in xrange(10):
    for b in xrange(20):
        if something(a, b):
            # Break the inner loop...
            break
    else:
        # Continue if the inner loop wasn't broken.
        continue
    # Inner loop was broken, break the outer.
    break

这使用了 for/else 结构，解释如下:为什么python在for和while循环之后使用'else'?

This uses the for / else construct explained at: Why does python use 'else' after for and while loops?

关键见解:只是似乎好像外循环总是中断.但如果内循环不中断，外循环也不会.

Key insight: It only seems as if the outer loop always breaks. But if the inner loop doesn't break, the outer loop won't either.

continue 语句是这里的魔法.它在 for-else 子句中.根据定义，如果没有内部中断，就会发生这种情况.在那种情况下，continue 巧妙地绕过了外部中断.

The continue statement is the magic here. It's in the for-else clause. By definition that happens if there's no inner break. In that situation continue neatly circumvents the outer break.

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