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

31
votes

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
4
pythonloopspython-2.7for-loopbreak
Rejected PEP: python.org/dev/peps/pep-3136 – mhlester
@mhlester what do you mean by rejected pep? – Vader
There was a proposal to name loops so you could break out of a specific one. It was rejected. The link has that discussion. – mhlester
Related post on naming loops – inspectorG4dget

4 Answers

56
votes

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.

18
votes

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
11
votes

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
1
votes

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