Python：我的除外條款確實太寬泛了嗎？

Question

我的代碼工作正常，但PyCharm在下面提到的except子句太寬泛。說實話，它也聞到了我的錯誤實現。

當我拼湊HTML <tr>時，我也必須添加到數據庫或更新，但事先並不知道遊戲是否完成。此外，尚未完成的遊戲在某些<td>中有不同的HTML標籤，需要不同的處理。

基本上，如果我們看看match_score_string和match_relevant_bit，我們告訴BeautifulSoup找到一個具有某個類別的<td>。如果遊戲已經完成，這個<td>將有一個score-time sc類，如果沒有，它將有一個score-time st類。如果它有一個，它就不會有另一個。

自從我編寫try-except子句以來已經有一段時間了，但是如果我記得正確的話，我必須使用它的原因是因爲當row.find無法找到HTML時，BS會拋出錯誤並暫停所有操作目的。

PyCharm抱怨是否合理？

# Get Match Score 
try: 
    match_score_string = row.find("td", class_="score-time sc").get_text() 
    match_string_split = match_score_string.split(" - ") 
    team_a_score = int(match_string_split[0]) 
    team_b_score = int(match_string_split[1]) 
    print(team_a_score) 
    print(team_b_score) 
except: 
    team_a_score = None 
    team_b_score = None 

# Get Match URL 
try: 
    match_relevant_bit = row.find("td", class_="score-time sc") 
    match_url = match_relevant_bit.find("a").get("href") 
    match_url_done = match_url.rsplit('?JKLMN') 
    match_url = match_url_done[0] 
    match_finished = True 

except: 

    match_relevant_bit = row.find("td", class_="score-time st") 
    match_url = match_relevant_bit.find("a").get("href") 
    match_url_done = match_url.rsplit('?JKLMN') 
    match_url = match_url_done[0] 
    match_finished = False 

Answer 1

你的except肯定是太寬泛了。在這些情況下，我不會否認你是否需要異常處理 - 例外情況非常惡劣，所以只要你認爲合適，就使用它們。然而，你並沒有主張你需要你的代碼來處理每可以想象的異常。除了可以掩蓋各種各樣的bug之外，一個裸露的。例如如果您在以後的版本中拼錯了某個變量名：

try: 
    match_score_string = row.find("td", class_="score-time sc").get_text() 
    match_string_split = match_score_string.split(" - ") 
    team_a_score = int(match_string_spilt[0]) # oops 
    team_b_score = int(match_string_split[1]) 
    print(team_a_score) 
    print(team_b_score) 
except: 
    team_a_score = None 
    team_b_score = None 

裸節選還可以防止用戶發送KeyboardInterrupt終止程序...

這些都只是2個例子，爲什麼你不想要除了 - 因爲由此可能掩蓋的編程錯誤的數量接近無限，我沒有足夠的時間來展示所有這些;-)。

相反，你應該指定你會遇到什麼情況例外：

try: 
    match_score_string = row.find("td", class_="score-time sc").get_text() 
    match_string_split = match_score_string.split(" - ") 
    team_a_score = int(match_string_spilt[0]) # oops 
    team_b_score = int(match_string_split[1]) 
    print(team_a_score) 
    print(team_b_score) 
except AttributeError: # If no row is found, accessing get_text fails. 
    team_a_score = None 
    team_b_score = None 

這樣，像您期望和你不掩蓋（太多）編程錯誤的代碼執行。你想要做的下一件事情就是儘可能地限制異常處理程序中的代碼量。

Answer 2

Try/except從句很棒。聽起來你不太經常使用它們。

try/except塊可以幫助您避免複雜如果繼續之前檢查的條件語句，或代碼中有時會令它不清楚你是什麼嘗試 ING做（見我做什麼有：P）。

有幾個例外，你可能會拖出你的代碼，其中一些可能比其他人更可能。見下：

try: 
    # This first line could have an AttributeError in two places 
    #  Maybe the row didn't parse quite correctly? find() won't work then. 
    #  Maybe you didn't find any elements? get_text() won't work then. 
    match_score_string = row.find("td", class_="score-time sc").get_text() 
          ^        ^
    # Same as here, you could get an AttributeError if match_score_string isn't a string. 
    #  I would say that isn't very likely in this case, 
    #  Especially if you handle the above line safely. 
    match_string_split = match_score_string.split(" - ") 

    # If either of these split strings contains no matches, you'll get an IndexError 
    # If either of the strings at the index contain letters, you may get a ValueError 
    team_a_score = int(match_string_split[0]) 
    team_b_score = int(match_string_split[1]) 

    # Theoretically, if you caught the exception from the above two lines 
    #  you might get a NameError here, if the variables above never ended up being defined. 
    print(team_a_score) 
    print(team_b_score) 
except: 
    # Can't really imagine much going wrong here though. 
    team_a_score = None 
    team_b_score = None 

正如你可能想象的那樣，捕獲幾種類型的異常可能更有用。這取決於您輸入的複雜性。

多個try/except塊在這裏也會有好處，特別是在處理這種情況下，如果發現錯誤並需要繼續執行該塊內的其餘代碼。