My sorting algorithm in python freezes sometimes during runtime, can someone take a look? -

basically i've been trying is, i'm picking out smallest , largest unsorted list, appending them new list, popping smallest , largest old unsorted list , doing process on , on until end sorted list. please take @ code .

import random import time  stack = [] #sorted list numbersarray = [] #unsorted list  usersize = int(input("how many digits want in array? ")) #numberofinputs limit = 0 counter = 0   while limit <= usersize:     numbersarray.append(random.randint(0,20)) #randomly input numbers array     limit = limit + 1  print(numbersarray) #prints current unsorted array start_time = time.time() #starts clock  subtractor = 0 #used later in code changing index while len(numbersarray) != 0:     = 0     largest = numbersarray[i]     size = len(numbersarray) -1     smallest = numbersarray[i]  while (i < len(numbersarray)):      if numbersarray[i] >= largest:         largest = numbersarray[i]         index =     elif numbersarray[i] <= smallest:         smallest = numbersarray[i]         indextwo =     = i+1  if (len(numbersarray) == 1): #this checks if there's 1 number left.     entry = int(stacksize/2 + 1)     stack.insert(entry,numbersarray[0])     break else:     if indextwo > index:         numbersarray.pop(indextwo)         numbersarray.pop(index)     elif index > indextwo:         numbersarray.pop(index)         numbersarray.pop(indextwo)  stacksize = len(stack) if stacksize == 0:     stack.append(smallest)     stack.append(largest) elif stacksize != 0:     stack.insert(stacksize-subtractor,largest) #the subtractor dynamically changing index of insertion.     stack.insert(0+subtractor,smallest) subtractor = subtractor + 1  print(stack) print("--- %s seconds ---" % (time.time() - start_time)) 

you have doubly nested while loop in scan whole array max , mins , proceed .pop elements list in arbitrary positions.

considering pop of o(n) complexity items not in end of list; approach highly inefficient , pass out/freeze large values of usersize. that's why, i'm guessing, "sometimes" in title happens when usersize large.

in short, case need find better algorithm solve problem.