给定以下代码(不起作用):
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
有办法解决这个问题吗?还是我必须先检查一次，跳出输入循环，然后再检查一次，如果用户满意，再跳出外部循环?
当前回答
要跳出多个嵌套循环，而不需要重构为函数，可以使用带有内置StopIteration异常的“模拟goto语句”:
try:
for outer in range(100):
for inner in range(100):
if break_early():
raise StopIteration
except StopIteration: pass
请参阅使用goto语句打破嵌套循环的讨论。
其他回答
# this version breaks up to a certain label
break_label = None
while True:
# snip: print out current state
while True:
ok = get_input("Is this ok? (y/n)")
if ok == "y" or ok == "Y":
break_label = "outer" # specify label to break to
break
if ok == "n" or ok == "N":
break
if break_label:
if break_label != "inner":
break # propagate up
break_label = None # we have arrived!
if break_label:
if break_label != "outer":
break # propagate up
break_label = None # we have arrived!
#do more processing with menus and stuff
尝试使用无限发电机。
from itertools import repeat
inputs = (get_input("Is this ok? (y/n)") for _ in repeat(None))
response = (i.lower()=="y" for i in inputs if i.lower() in ("y", "n"))
while True:
#snip: print out current state
if next(response):
break
#do more processing with menus and stuff
Break for外层和内部while循环:
while True:
while True:
print('Breaks inner "while" loop')
break # Here
print('Breaks outer "while" loop')
break # Here
或者，用if语句中断外部和内部while循环:
while True:
while True:
if True:
print('Breaks inner "while" loop')
break # Here
print('Breaks outer "while" loop')
break # Here
输出:
Breaks inner "while" loop
Breaks outer "while" loop
Break for outer和inner for循环:
for _ in iter(int, 1):
for _ in iter(int, 1):
print('Breaks inner "for" loop')
break # Here
print('Breaks outer "for" loop')
break # Here
或者，用if语句打破外部和内部for循环:
for _ in iter(int, 1):
for _ in iter(int, 1):
if True:
print('Breaks inner "for" loop')
break # Here
print('Breaks outer "for" loop')
break # Here
输出:
Breaks inner "for" loop
Breaks outer "for" loop
您可以定义一个变量(例如break_statement)，然后在发生两次中断条件时将其更改为不同的值，并在if语句中使用它来中断第二个循环。
while True:
break_statement=0
while True:
ok = raw_input("Is this ok? (y/n)")
if ok == "n" or ok == "N":
break
if ok == "y" or ok == "Y":
break_statement=1
break
if break_statement==1:
break
和上一台很像，但更紧凑。 (布尔值只是数字)
breaker = False #our mighty loop exiter!
while True:
while True:
ok = get_input("Is this ok? (y/n)")
breaker+= (ok.lower() == "y")
break
if breaker: # the interesting part!
break # <--- !
