Let's say you have some nested for-loop that you want to break out of from the inner loop:

x = default
for key, values in dict_of_sets: 
	for value in values: 
		if predicate(value): 
			x = key 
			break 2  # INVALID SYNTAX, SADLY...

Well, it turns out that Python supports for-else, so this can be made trivial:

x = default_value 
for key, values in dict_of_sets: 
	for value in values: 
		if predicate(key, value): 
			x = value 
			break  # THIS BREAKS BOTH LOOPS! 
	else: 
		continue 
	break

You don't need to know why this works to use it; but, if you do, here's how it works:

  • When the inner for-loop exhausts, its else-clause executes next, which continues the program through that iteration of the outer for-loop (quietly skipping the break statement on line 9).
  • If the inner for-loop is, instead, killed with the break on line 6, its else-clause is skipped, allowing the break statement on line 9 to execute and terminate the outer for-loop.

This can be used as much as you like:

for i in range(3): 
  for j in range(3): 
    for k in range(3): 
      for l in range(3): 
        for m in range(3): 
          for n in range(3): 
            print(i, j, k, l, m, n) 
            if input("Press enter to continue, or type anything to break out of all these loops.\n> "): 
              break  # THIS WILL BREAK ALL OF THE LOOPS! 
          else: 
            continue 
          break 
        else: 
          continue 
        break 
      else: 
        continue 
      break 
    else: 
      continue 
    break 
  else: 
    continue 
  break

 

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