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 

Answer 1

just indent your code correctly:

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