Python-сообщество

def fib(n):
  if n in [0, 1]:
    return 1
  else:
    return fib(n - 1) + fib(n - 2)

def fib(n):
  """the iterative implementation"""
  x, y = 0, 1
  for _ in range(n):
    x, y = y, x + y
  return y