stack.py

def new_stack(size):
    # our stack will be a list of [list, int] for [contents, head]
    # so stack[0] is contents
    #    stack[1] is head
    contents = [0] * size
    head = 0
    return [contents, head]

def is_full(stack):
    # this will not work
    return stack[1] > len(stack[0])
    
def is_empty(stack):
    return stack[1] == 0    

def push(stack, x):
    if is_full(stack):
        # fail silently, could also raise an error here instead
        return
    stack[0][stack[1]] = x
    stack[1] += 1
    
def pop(stack):
    if is_empty(stack):
        return
    stack[1] -= 1
    return stack[0][stack[1]]

if __name__ == "__main__":
    my_stack = new_stack(5)
    push(my_stack, 4)
    push(my_stack, 10)
    push(my_stack, 3)
    print(pop(my_stack)) # should print 3
    print(pop(my_stack)) # should print 10
    push(my_stack, 7)
    print(pop(my_stack)) # should print 7