Python - `break` out of all loops [duplicate]

问题

I am using multiple nested for loops. In the last loop there is an if statement. When evaluated to True all the for loops should stop, but that does not happen. It only breaks out of the innermost for loop, and than it keeps on going. I need all loops to come to a stop if the break statement is encountered.

My code:

for i in range(1, 1001):
    for i2 in range(i, 1001):
        for i3 in range(i2, 1001):
            if i*i + i2*i2 == i3*i3 and i + i2 + i3 == 1000:
                print i*i2*i3
                break

回答1:

You should put your loops inside a function and then return:

def myfunc():
    for i in range(1, 1001):
        for i2 in range(i, 1001):
            for i3 in range(i2, 1001):
                if i*i + i2*i2 == i3*i3 and i + i2 + i3 == 1000:
                    print i*i2*i3
                    return # Exit the function (and stop all of the loops)
myfunc() # Call the function

Using return immediately exits the enclosing function. In the process, all of the loops will be stopped.

回答2:

You can raise an exception

try:
    for a in range(5):
        for b in range(5):
            if a==b==3:
                raise StopIteration
            print b
except StopIteration: pass

回答3:

why not use a generator expression:

def my_iterator()
    for i in range(1, 1001):
        for i2 in range(i, 1001):
            for i3 in range(i2, 1001):
                yield i,i2,i3

for i,i2,i3 in my_iterator():
    if i*i + i2*i2 == i3*i3 and i + i2 + i3 == 1000:
        print i*i2*i3
        break

回答4:

Not sure if this the cleanest way possible to do it but you could do a bool check at the top of every loop.

do_loop = True

for i in range(1, 1001):
    if not do_loop:
        break
    for i2 in range(i, 1001):
        # [Loop code here]
        # set do_loop to False to break parent loops

来源：https://stackoverflow.com/questions/21293336/python-break-out-of-all-loops

标签

python

loops

python-2.7

for-loop

break