Fabonacci算法

　　　　

类思想实现

class Fabonacci:
    def __init__(self):
        self.b=[1,1] # 缓存计算结果

    def __call__(self,p):
        if p <= len(self.b): # 判断是否已经计算过
            return self.b[p-1]
        for v in range(len(self.b),p):
            self.b.append(self.b[v-1]+self.b[v-2])
        return self.b[p-1]

    def __len__(self):
        return len(self.b)

    def __getitem__(self,item): # item默认为positive integer,
        print(len(self),'&&&&&&&&&&&&&')
        if item<0:
            return None
        if item-1>len(self)-1: # 长度不足,调用__call__(self,p)计算
            self.__call__(item) # self(item)
        print(len(self),'&'*30)
        return self.b[item-1]

    def __iter__(self):
        return iter(self.b)

import time
start=time.time()
m=Fabonacci()
print(m(5))
end=time.time()
print(end-start)
print(m[7])

for pp in m:
    print(pp)