def factorial(n):
    if n == 0:
        return 1
    return n * factorial(n - 1)

def i_factorial(n):
    product = 1
    for k in range(1, n + 1):
        product *= k
    return product

for k in range(10):
    print '{}! = {:6d}, {:6d}'.format(k, factorial(k), i_factorial(k))

maze = (0, None,
        (1, None,
         (2, None,
          (3, None, (), ()),
          (4, None, (), ())),
         (5, None,
          (6, None, (), ()),
          ())),
        (7, None,
         (8, None, (), ()),
         (9, None,
          (10, None,
           (11, 'cheese', (), ()),
           ()),
          ())))

def explore(node, depth=0):
    if not node: # empty tuple
        print ' <' * depth, 'Nothing found'
        return False
    print ' >' * depth, 'Checking node', node[0]
    if node[1]: # check for non-empty/non-None 2nd element
        print ' *' * depth, 'Found', node[1], 'at node', node[0]
        return node[:2] # return tag and element
    return explore(node[2], depth + 1) or explore(node[3], depth + 1)

explore(maze)