如果在beautifulsoup中找不到元素，如何添加returnnone

import requests
from bs4 import BeautifulSoup

respond_timestamp=[]
for i in range(17,18):
    print(i)
    try:
        url='https://www.darooyab.ir/doctor/9/????-?????-???????page=' str(i)
        #print(url)
        response = requests.get(url).content.decode()
    except:
        continue
        
    soup = BeautifulSoup(response,'html.parser') 
    comment= soup.select('div.comment')
    #print( len(comment))
    
    for rt in [i for i in soup.select('div.comment')]:
        try:
            for out in [j.text for j in rt.select('div:nth-child(3) > span:nth-child(1) > label:nth-child(1)')]:
            #print(rt[1])
                pattern=r'???? ????? ?????? - ????? ??? ? ????'
                respond_timestamp.append(re.sub(pattern,'',out)) 
        except:
            respond_timestamp.append(None)
            
print(len(respond_timestamp)) 

我想附加respond_timestamp到串列中。的回傳值respond_timestamp可能為空，然后我使用try/except和append(None)，但None不會添加到串列中。因為串列的計數很重要。

我該怎么辦？

uj5u.com熱心網友回復：

注意 檢查/列印您的串列，它不是不會被附加的 None，而是最后缺少的“時間戳” - 基于您的示例

怎么了？

1. 主要問題是re模塊沒有匯入（看看你的例子）
2. 這些不必要的串列理解使代碼非常混亂并且除錯起來更加困難。此外，如果沒有responseComment不啟動您的回圈，因為它是一個空串列，這將使您try成功并且不會導致例外。

怎么修？

匯入re模塊以避免例外并更改您的 for 回圈 - 僅選擇一個元素來檢查您的try：

for rt in soup.select('div.comment'):
    try:
        out = rt.select_one('div:nth-child(3) > span:nth-child(1) > label:nth-child(1)').text
        pattern= '???? ????? ?????? - ????? ??? ? ????'
        respond_timestamp.append(re.sub(pattern,'',out)) 
    except Exception as ex:
        print(repr(ex))
        respond_timestamp.append(None) 

例子

請注意， 如果您的目標是生成字典，請在整個程序中完成，而不是通過壓縮多個串列，...

import requests
from bs4 import BeautifulSoup

data = []
for i in range(17,18):
    try:
        url='https://www.darooyab.ir/doctor/9/????-?????-???????page=' str(i)
        response = requests.get(url).content.decode()
    except:
        continue

    soup = BeautifulSoup(response,'lxml') 

    for c in soup.select('.comment'):
        # pattern=r'???? ????? ?????? - ????? ??? ? ????'
        # print(re.sub(pattern,'',c.select_one('div:nth-child(3) > span:nth-child(1) > label:nth-child(1)').text)) 
        data.append({
            'commentDate':c.span.text.split(' ')[1][1:-1],
            'commentText':c.div.text,
            'responseDate':responseDate.text.split(' ')[-1][1:-1] if (responseDate := c.select_one('.responseComment label')) else None,
            'responseText':responseText.text if (responseText := c.select_one('.responseComment .commentText')) else None,
        })

data

輸出

[{'commentDate': '1398/12/29',
  'commentText': '???? ?? ???? ?????? ??? ???????? ????  ?????  ? ???? ????? ?? ???? ????? ????? ????? ??? ??? ??? ???? ??? ?? ? ??? ?? . ??? ??? ??? ??? ?? ??? ?????? ????? ????? ??????? ?? ??? ???? ?? ???? ??? ????\r\n',
  'responseDate': None,
  'responseText': None},
 {'commentDate': '?????',
  'commentText': '?? ???? ???? ???? ???? ????. ?????? ?? ?? ?? ????? ????? ??? ??????????? ???? 1 ???? ?? ??? ? ?? ???? ?? ???? ??? ?? ???? . ????? ???????????????? ???? ??? ?? ???? ???? ????? ???. ????????? ',
  'responseDate': '1399/2/25',
  'responseText': '???? ????? ?? ??? ??? ???'},
 {'commentDate': '1398/12/28',
  'commentText': '???? . ?? ????? ?? ???? ??? ???? ? ????? ??? ?? ?? ?? ???? ?????? ???? . ???? ?? ?????????????? ? ??????????? ????? ???? . ???? ?? ????? ???? ???? ???? ?? ????? . ???????? ????? ???? ?? ???? ??? ?? ???? ?',
  'responseDate': '1399/2/25',
  'responseText': '???? ????? ?? ??? ??? ???'},
...]

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