的Python：list.pop（0）給出指數錯誤，而列表已滿

Question

所以我試圖找回的ñ商店列表，以使得它們的鄰居，然後，如果必要的話，鄰居的鄰居。以下是用於計算此列表的代碼，稱爲位置。商店的編號從1到10。

在這種情況下，每個商店有4個鄰居。這種關係在字典中被隨機設置，稱爲鄰居。

import random 

shops = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 

neighbours = {} 

for i in shops: 
    neighbours[i] = random.sample(shops, 4) 
    while i in neighbours[i]: 
     neighbours[i] = random.sample(shops, 4) 
print (neighbours) 
shop_zero = random.randrange(1,11) 
locations = [shop_zero] 
neighborhd = neighbours[locations[0]] 
n=10 
while len(locations) < n: 
    if not neighborhd: 
     print('if statement') 
     neighborhd = neighbours[random.choice(locations)] 
     print (neighborhd) 
    print('while loop') 
    ne = neighborhd.pop(0) 
    if ne not in locations: 
     locations.append(ne) 
print (locations) 

的問題是，代碼工作有時但常常給我一個索引錯誤：

IndexError: pop from empty list 

對於那些有興趣，以下是鄰居詞典輸出：

{1: [7, 5, 4, 9], 2: [5, 6, 3, 7], 3: [10, 8, 7, 6], 4: [7, 8, 10, 2], 5: [3, 6, 1, 9], 6: [5, 1, 10, 3], 7: [3, 8, 6, 2], 8: [10, 4, 9, 7], 9: [6, 5, 3, 2], 10: [3, 5, 8, 7]} 

我已經添加了一些打印語句以使工作示例更具信息性。正如我前面所說，它每隔一段時間都會有效，但大多數情況下會導致索引錯誤。 請幫忙？

P.S.我意識到，由此產生的列表並不總是給我的羣集，而是一個從鄰居到鄰居的路徑。這對我正在進行的項目來說很好。

Answer 1

我改變你的代碼調試的幫助，你可以看到下面。如果你運行這個，你會發現當拋出異常時，'鄰居'字典中的某些值有空列表。這意味着'鄰居'有可能被重新填充爲'鄰居'的空列表，所以仍然是空的。

import random 

shops = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 

neighbours = {} 

for i in shops: 
    neighbours[i] = random.sample(shops, 4) 
    while i in neighbours[i]: 
     neighbours[i] = random.sample(shops, 4) 
print (neighbours) 
shop_zero = random.randrange(1,11) 
locations = [shop_zero] 
neighborhd = neighbours[locations[0]] 
n=10 
while len(locations) < n: 
    if not neighborhd: 
     print('if statement') 
     neighborhd = neighbours[random.choice(locations)] 
     print (neighborhd) 
    print('while loop') 
    try: 
     ne = neighborhd.pop(0) 
    except IndexError: 
     raise IndexError("Attempt to pop from neighborhd which has content %s, formed from neighbours which has content %s" % (neighborhd, neighbours)) 
    if ne not in locations: 
     locations.append(ne) 
print (locations) 

Answer 2

基本上，你在neighborhd = neighbours[random.choice(locations)]有問題。它也返回空列表。所以你需要做一點改變。 if neighborhd:到pop之前只是檢查它不是一個空的列表。

import random 

shops = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 

neighbours = {} 

for i in shops: 
    neighbours[i] = random.sample(shops, 4) 
    while i in neighbours[i]: 
     neighbours[i] = random.sample(shops, 4) 
print (neighbours) 
shop_zero = random.randrange(1,11) 
locations = [shop_zero] 
neighborhd = neighbours[locations[0]] 
n=10 
while len(locations) < n: 
    if not neighborhd: 
     print('if statement') 
     neighborhd = neighbours[random.choice(locations)] 
     print (neighborhd) 
    print('while loop') 
    if neighborhd: 
     ne = neighborhd.pop(0) 
     if ne not in locations: 
      locations.append(ne) 
print (locations)