问题描述
我刚刚阅读了有关 lru_cache 装饰器的文章并进行了以下实验。
from functools import lru_cache
import time
def fib_wo_cache(n):
return n if n < 2 else fib_wo_cache(n-1) + fib_wo_cache(n-2)
begin = time.time()
fib_wo_cache(35)
end = time.time()
print("time it took without cache: ",end-begin)
@lru_cache(maxsize=2000)
def fib_w_cache(n):
return n if n < 2 else fib_wo_cache(n-1) + fib_wo_cache(n-2)
begin = time.time()
fib_w_cache(35)
end = time.time()
print("time it took with cache: ",end-begin)
结果让我吃惊：
time it took without cache: 4.684133052825928
time it took with cache: 4.4438371658325195
但是，一旦我通过只保留一个函数来一次测量一个缓存和非缓存函数，我得到：
not cached: 4.3182690143585205
cached: 0.00010395050048828125
缓存的后一个结果对我来说更有意义，因为它明显更快。缓存的两个结果之间的差异是如此巨大 - 你对我做错了什么有任何直觉吗？
谢谢！
解决方法
您犯了一个非常简单的错误 - 带缓存的 fib 在内部调用不带缓存的 fib。
试试
@lru_cache(maxsize=2000)
def fib_w_cache(n):
return n if n < 2 else fib_w_cache(n-1) + fib_w_cache(n-2)