else:语句当且仅当while循环不再满足它的条件时执行(在您的示例中，当n != 0为假时)。

所以输出是这样的:

5
4
3
2
1
what the...

else子句只在while条件为false时执行。

下面是一些例子:

例1:初始条件为false，因此执行else-clause。

i = 99999999

while i < 5:
    print(i)
    i += 1
else:
    print('this')

输出:

this

例2:while-condition i < 5永远不会变成false，因为i == 3打破了循环，所以else-clause没有执行。

i = 0

while i < 5:
    print(i)
    if i == 3:
        break
    i += 1
else:
    print('this')

输出:

0
1
2
3

例3:while-condition i < 5在i为5时变为false，因此执行else-clause。

i = 0

while i < 5:
    print(i)
    i += 1
else:
    print('this')

输出:

0
1
2
3
4
this

我知道这是个老问题，但是…

正如Raymond Hettinger所说，应该调用while/no_break而不是while/else。 如果你看一下这个片段，我发现它很容易理解。

n = 5
while n > 0:
    print n
    n -= 1
    if n == 2:
        break
if n == 0:
    print n

现在，我们不用在while循环后检查condition，而是用else替换它，然后去掉那个检查。

n = 5
while n > 0:
    print n
    n -= 1
    if n == 2:
        break
else:  # read it as "no_break"
    print n

我总是把它读成while/no_break来理解代码，这种语法对我来说更有意义。

如果while循环没有中断，则执行Else。

我有点喜欢用“跑步者”来比喻。

“else”就像越过终点线，与你是从赛道的起点还是终点出发无关。"else"只有当你在两者之间的某个地方中断时才不会执行。

runner_at = 0 # or 10 makes no difference, if unlucky_sector is not 0-10
unlucky_sector = 6
while runner_at < 10:
    print("Runner at: ", runner_at)
    if runner_at == unlucky_sector:
        print("Runner fell and broke his foot. Will not reach finish.")
        break
    runner_at += 1
else:
    print("Runner has finished the race!") # Not executed if runner broke his foot.

主要的用例是使用这种打破嵌套循环，或者如果你想只在循环没有在某处中断时运行某些语句(认为中断是一种不寻常的情况)。

例如，下面是一个关于如何在不使用变量或try/catch的情况下跳出内部循环的机制:

for i in [1,2,3]:
    for j in ['a', 'unlucky', 'c']:
        print(i, j)
        if j == 'unlucky':
            break
    else: 
        continue  # Only executed if inner loop didn't break.
    break         # This is only reached if inner loop 'breaked' out since continue didn't run. 

print("Finished")
# 1 a
# 1 b
# Finished

else子句只在while条件变为false时执行。如果跳出循环，或者引发异常，则不会执行该循环。

一种考虑它的方法是作为一个关于条件的if/else结构:

if condition:
    handle_true()
else:
    handle_false()

类似于循环结构:

while condition:
    handle_true()
else:
    # condition is false now, handle and go on with the rest of the program
    handle_false()

一个例子可能是:

while value < threshold:
    if not process_acceptable_value(value):
        # something went wrong, exit the loop; don't pass go, don't collect 200
        break
    value = update(value)
else:
    # value >= threshold; pass go, collect 200
    handle_threshold_reached()

当while-condition的值为false时，else子句将被执行。

从文档中可以看到:

The while statement is used for repeated execution as long as an expression is true: while_stmt ::= "while" expression ":" suite ["else" ":" suite] This repeatedly tests the expression and, if it is true, executes the first suite; if the expression is false (which may be the first time it is tested) the suite of the else clause, if present, is executed and the loop terminates. A break statement executed in the first suite terminates the loop without executing the else clause’s suite. A continue statement executed in the first suite skips the rest of the suite and goes back to testing the expression.