def hanoi(n, source, helper, target):
if n > 0:
# move tower of size n - 1 to helper:
hanoi(n - 1, source, target, helper)
# move disk from source peg to target peg
if source:
target.append(source.pop())
# move tower of size n-1 from helper to target
hanoi(n - 1, helper, source, target)
source = [4,3,2,1]
target = []
helper = []
hanoi(len(source),source,helper,target)
print( source, helper, target)