Python腳本崩潰，我不知道爲什麼

Question

所以我有2個python程序確定斐波納契數字。一個使用memoinization，另一個不使用。兩者都可以工作，並且能夠在給出輸入時確定數字。

但是，我需要對它們進行計時，這是第三個程序進入的地方。我已經確定了第一個fib數到第三十的兩個函數。當我運行第三個程序的時候，它似乎在計算第九個數字的時候就是廢話，我不知道爲什麼。

有人可以幫我嗎？我對所有3個項目下面的代碼（和錯誤）

感謝

---

計劃1

#!/usr/bin/python 

import sys 

def fib(n): 
    if n == 0: 
     return 0 
    elif n == 1: 
     return 1 
    else: 
     return fib(n-1) + fib(n-2) 

numIn = int(sys.argv[1]) 
result = fib(numIn) 

print 'The %dth fibonacci number is %d' % (numIn, result) 

---

方案2：

#!/usr/bin/python 

import sys 

cache = [None]*100 

def fib(n): 

    if n in cache: 
     return cache[n] 

    else: 
     if n < 2: 
      cache[n] = n 
     else: 
      cache[n] = fib(n-1) + fib(n-2) 

     return cache[n] 

numIn = int(sys.argv[1]) 
result = fib(numIn) 

print 'The %dth fibonacci number is %d' % (numIn, result) 

---

方案三：

#!/usr/bin/python 

import sys,timeit,time 

for i in range(1, 30): 
     t1 = timeit.Timer('fib(%s)' % i, 'from problem1 import fib').timeit() 
     t2 = timeit.Timer('fib(%s)' % i, 'from problem2 import fib').timeit() 
     print 'The time for the %d th number is %f (Problem 1 - No Memo' % (i,t1) 
     print 'The time for the %d th number is %f (Problem 1 - Memo' % (i,t2) 

---

錯誤：

The 5th fibonacci number is 5 
The 5th fibonacci number is 5 
The time for the 1 th number is 0.215671 (Problem 1 - No Memo 
The time for the 1 th number is 0.247929 (Problem 1 - Memo 
The time for the 2 th number is 0.606024 (Problem 1 - No Memo 
The time for the 2 th number is 0.269888 (Problem 1 - Memo 
The time for the 3 th number is 1.027372 (Problem 1 - No Memo 
The time for the 3 th number is 0.298666 (Problem 1 - Memo 
The time for the 4 th number is 1.839900 (Problem 1 - No Memo 
The time for the 4 th number is 4.466314 (Problem 1 - Memo 
The time for the 5 th number is 3.117439 (Problem 1 - No Memo 
The time for the 5 th number is 0.308327 (Problem 1 - Memo 
The time for the 6 th number is 5.178429 (Problem 1 - No Memo 
The time for the 6 th number is 8.496127 (Problem 1 - Memo 
The time for the 7 th number is 8.486079 (Problem 1 - No Memo 
The time for the 7 th number is 12.532179 (Problem 1 - Memo 
The time for the 8 th number is 13.571108 (Problem 1 - No Memo 
The time for the 8 th number is 0.321315 (Problem 1 - Memo 
Traceback (most recent call last): 
    File "./problem3.py", line 7, in <module> 
    t2 = timeit.Timer('fib(%s)' % i, 'from problem2 import fib').timeit() 
    File "/usr/lib/python2.7/timeit.py", line 195, in timeit 
    timing = self.inner(it, self.timer) 
    File "<timeit-src>", line 6, in inner 
    File "problem2.py", line 18, in fib 
    cache[n] = fib(n-1) + fib(n-2) 
TypeError: unsupported operand type(s) for +: 'NoneType' and 'int' 

Answer 1

if n in cache是錯誤的邏輯。你可能想if cache[n] is not None

n應該代表第n個斐波那契數，所以緩存是存儲斐波那契數，他們不是indicies。