How to continue in nested loops in Python

59
votes

How can you continue the parent loop of say two nested loops in Python?

for a in b:
    for c in d:
        for e in f:
            if somecondition:
                <continue the for a in b loop?>

I know you can avoid this in the majority of cases but can it be done in Python?

6
python
any reason to not just use break ? - Jon Clements♦
Use break to leave the inner loop - this'll immediately continue in the outer loop. - TyrantWave
There's another similar question: stackoverflow.com/questions/189645/… - esycat
@JonClements I've fixed the example to actually need the continue. - James

6 Answers

52
votes
  1. Break from the inner loop (if there's nothing else after it)
  2. Put the outer loop's body in a function and return from the function
  3. Raise an exception and catch it at the outer level
  4. Set a flag, break from the inner loop and test it at an outer level.
  5. Refactor the code so you no longer have to do this.

I would go with 5 every time.

20
votes

Here's a bunch of hacky ways to do it:

  1. Create a local function

    for a in b:
    def doWork():
        for c in d:
            for e in f:
                if somecondition:
                    return # <continue the for a in b loop?>
    doWork()

    A better option would be to move doWork somewhere else and pass its state as arguments.

  2. Use an exception

    class StopLookingForThings(Exception): pass

for a in b:
    try:
        for c in d:
            for e in f:
                if somecondition:
                    raise StopLookingForThings()
    except StopLookingForThings:
        pass
12
votes
from itertools import product
for a in b:
    for c, e in product(d, f):
        if somecondition:
            break
7
votes

You use break to break out of the inner loop and continue with the parent

for a in b:
    for c in d:
        if somecondition:
            break # go back to parent loop
1
votes

Looking at All the answers here its all different from how i do it\n Mission:continue to while loop if the if condition is true in nested loop

chars = 'loop|ing'
x,i=10,0
while x>i:
    jump = False
    for a in chars:
      if(a = '|'): jump = True
    if(jump==True): continue
0
votes

use a boolean flag

problem = False
for a in b:
  for c in d:
    if problem:
      continue
    for e in f:
        if somecondition:
            problem = True