# How can I stop a While loop?

### Question

I wrote a `while loop` in a function, but don't know how to stop it. When it doesn't meet its final condition, the loop just go for ever. How can I stop it?

``````def determine_period(universe_array):
period=0
tmp=universe_array
while True:
tmp=apply_rules(tmp)#aplly_rules is a another function
period+=1
if numpy.array_equal(tmp,universe_array) is True:
break    #i want the loop to stop and return 0 if the
#period is bigger than 12
if period>12:  #i wrote this line to stop it..but seems it
#doesnt work....help..
return 0
else:
return period
``````
1
11
12/23/2015 12:27:26 AM

``````def determine_period(universe_array):
period=0
tmp=universe_array
while True:
tmp=apply_rules(tmp)#aplly_rules is a another function
period+=1
if numpy.array_equal(tmp,universe_array) is True:
return period
if period>12:  #i wrote this line to stop it..but seems its doesnt work....help..
return 0
else:
return period
``````

You need to understand that the `break` statement in your example will exit the infinite loop you've created with `while True`. So when the break condition is True, the program will quit the infinite loop and continue to the next indented block. Since there is no following block in your code, the function ends and don't return anything. So I've fixed your code by replacing the `break` statement by a `return` statement.

Following your idea to use an infinite loop, this is the best way to write it:

``````def determine_period(universe_array):
period=0
tmp=universe_array
while True:
tmp=apply_rules(tmp)#aplly_rules is a another function
period+=1
if numpy.array_equal(tmp,universe_array) is True:
break
if period>12:  #i wrote this line to stop it..but seems its doesnt work....help..
period = 0
break

return period
``````
16
12/15/2008 3:04:14 PM

``````def determine_period(universe_array):
period=0
tmp=universe_array
while period<12:
tmp=apply_rules(tmp)#aplly_rules is a another function
if numpy.array_equal(tmp,universe_array) is True:
break
period+=1

return period
``````