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

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

其他回答

由于这个问题已经成为进入特定循环的标准问题,我想用Exception给出我的答案。

虽然在多循环构造中不存在名为“循环中断”的标签,但我们可以使用用户定义异常来中断到我们选择的特定循环。考虑下面的例子,让我们在6进制编号系统中打印所有最多4位的数字:

class BreakLoop(Exception):
    def __init__(self, counter):
        Exception.__init__(self, 'Exception 1')
        self.counter = counter

for counter1 in range(6):   # Make it 1000
    try:
        thousand = counter1 * 1000
        for counter2 in range(6):  # Make it 100
            try:
                hundred = counter2 * 100
                for counter3 in range(6): # Make it 10
                    try:
                        ten = counter3 * 10
                        for counter4 in range(6):
                            try:
                                unit = counter4
                                value = thousand + hundred + ten + unit
                                if unit == 4 :
                                    raise BreakLoop(4) # Don't break from loop
                                if ten == 30: 
                                    raise BreakLoop(3) # Break into loop 3
                                if hundred == 500:
                                    raise BreakLoop(2) # Break into loop 2
                                if thousand == 2000:
                                    raise BreakLoop(1) # Break into loop 1

                                print('{:04d}'.format(value))
                            except BreakLoop as bl:
                                if bl.counter != 4:
                                    raise bl
                    except BreakLoop as bl:
                        if bl.counter != 3:
                            raise bl
            except BreakLoop as bl:
                if bl.counter != 2:
                    raise bl
    except BreakLoop as bl:
        pass

当我们打印输出时,我们永远不会得到任何单位位是4的值。在这种情况下,在同一个循环中引发BreakLoop(4)并捕获时,我们不会中断任何循环。类似地,当十位有3时,我们使用BreakLoop(3)进入第三个循环。当百位是5时,我们使用BreakLoop(2)进入第二个循环,当千位是2时,我们使用BreakLoop(1)进入第一个循环。

简而言之,在内部循环中引发异常(内置或用户定义),并在循环中从您想恢复控件的位置捕获它。如果想从所有循环中中断,可以在所有循环之外捕获异常。(我没有举例说明)。

通过使用函数:

def myloop():
    for i in range(1,6,1):  # 1st loop
        print('i:',i)
        for j in range(1,11,2):  # 2nd loop
            print('   i, j:' ,i, j)
            for k in range(1,21,4):  # 3rd loop
                print('      i,j,k:', i,j,k)
                if i%3==0 and j%3==0 and k%3==0:
                    return  # getting out of all loops

myloop()

尝试通过注释掉返回值来运行上面的代码。

不使用任何函数:

done = False
for i in range(1,6,1):  # 1st loop
    print('i:', i)
    for j in range(1,11,2):  # 2nd loop
        print('   i, j:' ,i, j)
        for k in range(1,21,4):  # 3rd loop
            print('      i,j,k:', i,j,k)
            if i%3==0 and j%3==0 and k%3==0:
                done = True
                break  # breaking from 3rd loop
        if done: break # breaking from 2nd loop
    if done: break     # breaking from 1st loop

现在,首先按原样运行上面的代码,然后尝试从底部注释掉包含break的每一行。

# 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

我个人会做的是使用一个boolean,当我准备跳出外部循环时切换。例如

while True:
    #snip: print out current state
    quit = False
    while True:
        ok = input("Is this ok? (y/n)")
        if ok.lower() == "y":
            quit = True
            break # this should work now :-)
        if ok.lower() == "n":
            quit = True
            break # This should work too :-)
    if quit:
        break
    #do more processing with menus and stuff

尽量减少对OP的问题的改变,我只是在打破第一个for循环之前添加了一个标志,并检查外部循环上的标志,看看我们是否需要再次刹车。

break_2 = False
while True:
    # Snip: print out current state
    if break_2: break
    while True:
        ok = get_input("Is this ok? (y/n)")
        if ok.lower() == "y": break_2 = True
        if break_2: break
        if ok.lower() == "n": break
    # Do more processing with menus and stuff