How to break out of multiple loops?

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Given the following code (that doesn't work):

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

Is there a way to make this work? Or do I have do one check to break out of the input loop, then another, more limited, check in the outside loop to break out all together if the user is satisfied?

My first instinct would be to refactor the nested loop into a function and use return to break out.

How to break out of nested loops?, In your example break statement will take you out of while(b) loop Using a label you can break out of both loops: take a look at this example taken from The java break statement won't take you out of multiple nested loops. Put the loops into a function, and return from the function to break the loops. This is unsatisfying because the loops might not be a natural place to refactor into a new function, and maybe you need access to other locals during the loops. Raise an exception and catch it outside the double loop. This is using exceptions as a form of goto.

Here's another approach that is short. The disadvantage is that you can only break the outer loop, but sometimes it's exactly what you want.

for a in xrange(10):
    for b in xrange(20):
        if something(a, b):
            # Break the inner loop...
            break
    else:
        # Continue if the inner loop wasn't broken.
        continue
    # Inner loop was broken, break the outer.
    break

This uses the for / else construct explained at: Why does python use 'else' after for and while loops?

Key insight: It only seems as if the outer loop always breaks. But if the inner loop doesn't break, the outer loop won't either.

The continue statement is the magic here. It's in the for-else clause. By definition that happens if there's no inner break. In that situation continue neatly circumvents the outer break.

Break statement inside two while loops, Place a break inside the inner most loop, then for each outer loop, add continue in the else block, which skips the remainder of the loop, then break after the end of  Or do I have do one check to break out of the input loop, then another, more limited, check in the outside loop to break out all together if the user is satisfied? Edit-FYI: get_input is a short function I wrote that supports showing a prompt and default values and all that fanciness and returns stdin.readline().strip()

PEP 3136 proposes labeled break/continue. Guido rejected it because "code so complicated to require this feature is very rare". The PEP does mention some workarounds, though (such as the exception technique), while Guido feels refactoring to use return will be simpler in most cases.

How to break out of multiple loops, By the way, there is a better way to do the same thing, by externalizing the code of nested loop into a method and using return statement for coming out of the loop. A lot of noise here concerns the breaking out of the loop, rather than the work itself. The sophisticated approach is to get rid of, or at least hide away, the double loop. Looked at another way, this code is really iterating over one sequence of things, a sequence of pairs.

First, ordinary logic is helpful.

If, for some reason, the terminating conditions can't be worked out, exceptions are a fall-back plan.

class GetOutOfLoop( Exception ):
    pass

try:
    done= False
    while not done:
        isok= False
        while not (done or isok):
            ok = get_input("Is this ok? (y/n)")
            if ok in ("y", "Y") or ok in ("n", "N") : 
                done= True # probably better
                raise GetOutOfLoop
        # other stuff
except GetOutOfLoop:
    pass

For this specific example, an exception may not be necessary.

On other other hand, we often have "Y", "N" and "Q" options in character-mode applications. For the "Q" option, we want an immediate exit. That's more exceptional.

How to break from nested loop in Java, A break statement in a loop (if the break is not part of a switch case) always breaks out of only the loop in which the break is executed. If the break appears inside  If not this then you could use flags to break out of deep nested loops. Another approach to breaking out of a nested loop is to factor out both loops into a separate function, and return from that function when you want to exit. Summarized - to break out of nested loops: use goto; use flags; factor out loops into separate function calls

I tend to agree that refactoring into a function is usually the best approach for this sort of situation, but for when you really need to break out of nested loops, here's an interesting variant of the exception-raising approach that @S.Lott described. It uses Python's with statement to make the exception raising look a bit nicer. Define a new context manager (you only have to do this once) with:

from contextlib import contextmanager
@contextmanager
def nested_break():
    class NestedBreakException(Exception):
        pass
    try:
        yield NestedBreakException
    except NestedBreakException:
        pass

Now you can use this context manager as follows:

with nested_break() as mylabel:
    while True:
        print "current state"
        while True:
            ok = raw_input("Is this ok? (y/n)")
            if ok == "y" or ok == "Y": raise mylabel
            if ok == "n" or ok == "N": break
        print "more processing"

Advantages: (1) it's slightly cleaner (no explicit try-except block), and (2) you get a custom-built Exception subclass for each use of nested_break; no need to declare your own Exception subclass each time.

Which loop does 'break' exit in nested for loops in C? Please provide , to search would take more time and resources while we don't need the extra information. That's why we want to break out of the nested loop. set that variable true in the first loop, when you want to break. then you can check in the outer loop, that whether the condition is set then break from the outer loop as well.

Breaking Out of Nested Loops, Swift has a built-in break keyword that escapes the current loop you're in, but what happens if you're in two loops or more and want to break out  Accepted Answer. This functionality is not availble when using the function BREAK. BREAK will only break out of the loop in which it was called. As a workaround, you can use a flag variable along with BREAK to break out of nested loops.

How to break out of multiple loop levels using labeled statements , Breaking out of a loop. The C++ statement called break provides a way to break out a loop early. The break statement is placed within the body of the loop  the best way is -. 1) Sort the both array which are used in first and second loop. 2) if item matched then break the inner loop and hold the index value. 3) when start next iteration start inner loop with hold index value.

Chapter 5: Nested loops, Which loop to use?, BREAK will only break out of the loop in which it was called. As a workaround, you can use a flag variable along with BREAK to break out of nested loops. flag=​0  I'm having problem with nested loop. I have multiple number of posts, and each post has multiple number of images. I want to get total of 5 images from all posts. So I am using nested loop to get the images, and want to break the loop when the number reaches to 5. The following code will return the images, but does not seem to break the loop.

Comments
  • Why doesn't Python just have 'break(n)' where n is the number of levels you want to break out of.
  • C++ is nice here with goto if you're nestled deep in a lot of loops
  • This is another thought I had, since a get_input_yn() function would be useful elsewhere too, I'm sure.
  • agreed in this specific case, but in the general case of 'I have nested loops, what do I do' refactoring may not make sense.
  • using an exception may be easier when you must yield instead of using return, however you probably should be using itertools.islice() in such a case.
  • Its usually possible to refactor the inner loop into its own method, that returns true to continue, false to break the outer loop. while condition1: / if not MyLoop2(params): break. An alternative is to set a boolean flag, that is tested at both levels. more = True / while condition1 and more: / while condition2 and more: / if stopCondition: more = False / break / ...
  • I agree that striving to use return is the right approach. And the reasoning is that, according to the Zen of Python, "flat is better than nested". We have three levels of nesting here and if that starts to get in the way, it is time to reduce the nesting or at least extract the whole nesting into a function of its own.
  • @eugeney Why not? The first break will get out of the inner loop.
  • @eugeney I feel like I am missing something here. Can you post an example?
  • @Mingliang that can go before the continue.
  • @RishitBansal Although this is a deep cut: The outer loop does matter because the inner break condition something(a, b) depends on a too. The outer loop may run as long as something(a, b) is not True.