斐波那契数列

递归生成斐波那契数列

def fib(n:int):
    if n <2:
       return  n
    return fib(n-1) + fib(n-2)

给递归加个缓存

cache = {}
def fib(n:int):
  if n<2:
      return n
  result = cache.get(n,None)
  if result is None:
      cache[n] = fib(n-1) + fib(n-2)
      return cache[n]
  return result

创建斐波那契数列迭代器

class Fib:
  def __init__(self,n:int):
      self.stop = n
      self.index = 1
      self.a,self.b = 0,1

  def __iter__(self):
      return self

  def __next__(self,):
      if self.index <= self.stop:
          self.a,self.b = self.b ,self.a+self.b
          self.index +=1
          return self.a
      raise StopIteration