IndexError：列表索引超出功能的Python範圍

Question

我試着在這個網站上看，但我找不到我的程序到底出了什麼問題。它一直到13或data_list [25]，但它會吐出IndexError消息。

def rlEncode(n, z, data_list): 
    while data_list[n] == data_list[n+1]: 
     z = z + 1 
     n = n + 1 
    while data_list[n] != data_list[n+1]: 
     return (n, z) 

def unitTest(): 
    counter = 0 
    n = 0 
    z = 1 
    data_list = [1,1,1,1,1,3,3,5,5,5,5,5,5,6,8,8,1,1,1,5,5,5,5,13,14, 14] 
    compress_list = [ ] 
    while counter < len(data_list): 
     rlEncode(n, z, data_list) 
     x, y = rlEncode(n, z, data_list) 
     compress = [data_list[x], y] 
     counter = counter + 1 
     compress_list = compress_list + compress 
     n = x+1 
     z = 1 
     continue 
    print("list: ", data_list) 
    print("compressed: ", compress_list) 

Answer 1

在你rlEncode功能，你遞增n過高後檢查while條件：

def rlEncode(n, z, data_list): 
    while data_list[n] == data_list[n+1]: 
     z = z + 1 
     n = n + 1 

第一次檢查data_list[n] == data_list[n + 1]它的確定......但那麼你就n = n + 1，去回去檢查while的情況。此時，如果n是25，則data_list[n + 1]會給您一個索引錯誤，因爲data_list[25 + 1]不存在。

您可以通過在n = n + 1之後添加打印線print(n, len(data_list))來檢查此問題。

所以，無論是確保你只能從0迭代到24，或者確保你做這樣的事情：

if n == len(data_list) - 1: 
    break 

你總是要保持你的陣列的上界記住，當你正在做的事情一樣list[n + 1]算法中的任何地方。

---

劇透：以下解決方案：

爲了讓你的代碼的工作，我做了兩個變化：

def rlEncode(n, z, data_list): 
    # Make sure we don't overrun our list length: 
    while n < len(data_list) - 1 and data_list[n] == data_list[n + 1]: 
     z += 1 
     n += 1 
    return (n, z) 

def unitTest(): 
    counter = 0 
    n = 0 
    z = 1 
    data_list = [1,1,1,1,1,3,3,5,5,5,5,5,5,6,8,8,1,1,1,5,5,5,5,13,14,14] 
    compress_list = [] 
    while n < len(data_list) - 1: # Use n here, not counter 
     rlEncode(n, z, data_list) 
     x, y = rlEncode(n, z, data_list) 
     compress = [data_list[x], y] 
     counter = counter + 1 
     compress_list = compress_list + compress 
     n = x + 1 
     z = 1 
    print("list: ", data_list) 
    print("compressed: ", compress_list) 

unitTest() 

('list: ', [1,1,1,1,1, 3,3, 5,5,5,5,5,5, 6, 8,8, 1,1,1, 5,5,5,5, 13, 14,14])
('compressed: ', [1,5, 3,2, 5,6, 6,1, 8,2, 1,3, 5,4, 13,1, 14,2])