UnboundLocalError：分配

Question

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convert list to string to insert into my sql in one row in python scrapy

我試圖寫HTML頁面直接到MySQL數據庫中提取數據之前引用局部變量「項目」。但過去工作的代碼不再這樣做。有人可以幫我嗎？

def parse(self, response): 
    hxs = HtmlXPathSelector(response) 
    sites = hxs.select('//ul/li') 
    con = MySQLdb.connect(
     host="localhost", 
     user="dreamriks", 
     passwd="dreamriks", 
     db="scraped_data" 
    ) 
    cur = con.cursor() 
    for site in sites: 
     items = [site.select('//h2').extract()] 
     item = [site.select('//h3').extract()] 
     meta = [site.select('//meta').extract()] 
    for index in range (len(items)):    #<-- exception raises here 
     str = items[index] 
     cur.execute("""Insert into h2_meta(h2) Values(%s)""",(str)) 
    con.commit() 
    con.close() 

上面的代碼提供了以下錯誤：

exceptions.UnboundLocalError: local variable 'items' referenced before assignment 

Answer 1

你的縮進被打破。縮進塊

for index in range (len(items)): 
    str = items[index] 
    cur.execute("""Insert into h2_meta(h2) Values(%s)""",(str)) 

剩餘4個空格。

Answer 2

看起來你有一個縮進問題。 for index in range(len(items))是部分的for site in sites循環，對吧？

for site in sites: 
     items = [site.select('//h2').extract()] 
     item = [site.select('//h3').extract()] 
     meta = [site.select('//meta').extract()] 
     for index in range (len(items)):    # <-- make sure this has same 
      str = items[index]      # level of indenting as previous lines 
      cur.execute("""Insert into h2_meta(h2) Values(%s)""",(str)) 

Answer 3

如果for site in sites:不重複，因爲sites爲空，則items永遠不會被初始化。

當您在for index in range (len(items)):中引用它時，代碼假設items已初始化。