列表索引超出範圍錯誤，同時使用for循環中的if語句

Question

我是python新手;我一直在JavaScript編碼，所以我不習慣我得到的所有錯誤。

我試圖用for循環將屬性添加到空對象，但我得到一個錯誤，指出列表索引超出範圍。當我在for循環中添加if語句時，該錯誤似乎正在發生。雖然我沒有使用索引來遍歷seat_info數組。請幫我理解爲什麼會發生這種情況，謝謝！

seats_info = ['\n1,133,0,A', '\n1,133,2,C', '\n1,133,1,B', '\n1,133,4,E', '\n1,133,3,D', '\n2,132,0,24', '\n2,132,1,25', '\n2,132,2,26'] 

    def read_manifest(self, manifest): 
    file = manifest_dir + '/' + manifest 
    data = open(file, 'r') 
    seats_info = data.read().split('\r')[1:] 
    data.close() 

    self.seat_information = {} 
    for seat_info in seats_info: 
     one_seat = seat_info.split(',') 
     section_id = one_seat[0][1:] 
     one_seat.remove(one_seat[0]) 
     one_seat.insert(0, section_id) 

     if one_seat[1] not in self.seat_information: 
      self.seat_information[one_seat[1]] = [one_seat] 
     else: 
      self.seat_information[one_seat[1]].append(one_seat) 


     Error Message that I received 

     Traceback (most recent call last): 
     File "path/normalizer.py", line 75, in <module> 
normalizer.read_manifest(citifield) 
     File "path/normalizer.py", line 36, in read_manifest 
    if one_seat[1] not in self.seat_information: 
    IndexError: list index out of range 

Answer 1

在數據文件中插入空白行以重現錯誤。

section_id = one_seat[0][1:] 
one_seat[0] = section_id 

此時，one_seat = [ '']，所以沒有one_seat [1]

if one_seat[1] ... 

因此列表索引超出範圍被正確地上升。相反，當您使用硬編碼索引時，您可能需要驗證您的假設是否成立。下面是一個示例重新寫：

def execute(): 
    seats_info = ['\n', '\n1,133,0,A', '\n1,133,2,C', '\n1,133,1,B', '\n1,133,4,E', '\n1,133,3,D', '\n2,132,0,24', '\n2,132,1,25', '\n2,132,2,26'] 
    for seat_info in seats_info: 
     one_seat = seat_info.split(',') 
     if len(one_seat): 
      section_id = one_seat[0][1:] 
      one_seat[0] = section_id 
      # maybe check for a legal section_id here? 
      if len(one_seat) > 1: 
       row_id = one_seat[1]     
       if row_id not in seat_information: 
        seat_information[row_id] = [one_seat] 
       else: 
        seat_information[row_id].append(one_seat) 


seat_information = {} 
execute() 
for row, seats in seat_information.items(): 
    print "row", row 
    for seat in seats: 
     print "seat:", seat 

Answer 2

雖然肯尼·奧斯特羅姆的解決方案是很好，我真的建議預處理的數據文件中讀取它通過這種方式後，你就不必不斷地檢查假設，並簡化了代碼。具體來說，我想到了以下幾點：

seats_info = ['\n', '\n1,133,0,A', '\n1,133,2,C', '\n1,133,1,B', '\n1,133,4,E', '\n1,133,3,D', '\n2,132,0,24', '\n2,132,1,25', '\n2,132,2,26'] 

#remove new line and other markup characters 
seats_info = [str.strip(s) for s in seats_info] 

#remove elements that have no content:  
seats_info = [s for s in seats_info if len(s)>0] 

所以現在，seats_info是清潔，你會不會引發錯誤：

In [21]: seats_info 
Out[21]: 
['1,133,0,A', 
'1,133,2,C', 
'1,133,1,B', 
'1,133,4,E', 
'1,133,3,D', 
'2,132,0,24', 
'2,132,1,25', 
'2,132,2,26'] 

由於您目前索引了\n但現在你不必，你必須簡化你的數據提取環路：

for seat_info in seats_info: 
    one_seat = seat_info.split(',') 
    section_id = one_seat[0] 

    if one_seat[1] not in seat_information: 
     self.seat_information[one_seat[1]] = [one_seat] 
    else: 
     self.seat_information[one_seat[1]].append(one_seat) 

最後，我強烈建議您使用with聲明閱讀您的數據，因爲在眼睛上更容易，我會說更多Pythonic。具體來說，請考慮您的read_manifest函數的以下定義：

def read_manifest(self, manifest): 
    file = manifest_dir + '/' + manifest 

    #read in the file: 
    with open(file, 'r') as f: 
     #because we later use str.strip, you don't need to do [1:] to get rid of \r 
     seats_info = f.read().split('\r') 

    #pre-process: 
    seats_info = [str.strip(s) for s in seats_info]  
    seats_info = [s for s in seats_info if len(s)>0]