python - 索引错误: list index out of range (in query results)

Question

我在理解如何使用查询结果时遇到问题。我问了大约六个问题，但我仍然不明白。我从以前的代码中复制并使其以某种方式工作，但由于我不理解基本概念，如果我进行微小的更改，代码就会崩溃。如果您能告诉我您如何想象这里发生的事情并向我解释，我将非常感激。谢谢。

class ReceiveEmail(InboundMailHandler):
    def receive(self, message):
        logging.info("Received email from %s" % message.sender)
        plaintext = message.bodies(content_type='text/plain')
        for text in plaintext:
            txtmsg = ""
            txtmsg = text[1].decode()
            logging.info("Body is %s" % txtmsg)
            logging.info("CC email is %s" % ((message.cc).split(",")[1]))            

        query = User.all()           
        query.filter("userEmail =",  ((message.cc).split(",")[1])) 
        results = query.fetch(1)                   

        for result in results:                     
            result.userScore += 1                  

        um = results[0]                            
        um.userScore = result.userScore            
        um.put()

在这段代码中，据我了解，查询从抄送列表中获取第二个电子邮件地址并获取结果。

然后我将 userScore 加 1。

接下来，我想更新数据存储中的此项，所以我说

        um = results[0]                            
        um.userScore = result.userScore            
        um.put()

但这会给出索引超出范围的错误:

um = results[0]
IndexError: list index out of range

为什么？我想象 results[0] 是结果的第零项。为什么超出范围？我唯一能想到的是，该列表可能是 None。但我不明白为什么。它必须具有已获取的 1 项。

此外，如果我尝试通过将索引从 [1] 更改为 [0] 来测试第一个电子邮件地址

query.filter("userEmail =",  ((message.cc).split(",")[0]))

然后我没有得到IndexError。

我在这里做错了什么？

谢谢!

编辑

查看评论:

(message.cc).split(",")[0]) 

在电子邮件前面留了一个空格(从第二封电子邮件开始)，因此查询与它们不匹配；

>>> cc.split(",")
['cc12@example.com', ' cc13@example.com', ' cc13@example.com']

在逗号后添加空格解决了问题:

>>> listcc = cc.split(", ")
>>> listcc
['cc12@example.com', 'cc13@example.com', 'cc13@example.com']
>>> 

Answer 1

要理解代码，请将其分解并逐段查看:

class ReceiveEmail(InboundMailHandler):
    def receive(self, message):
        logging.info("Received email from %s" % message.sender)

        # Get a list of CC addresses.  This is basically a for loop.
        cc_addresses = [address.strip() for address in message.cc.split(",")]
        # The CC list goes with the message, not the bodies.
        logging.info("CC email is %s" % (cc_addresses))

        # Get and iterate over all of the *plain-text* bodies in the email.
        plaintext = message.bodies(content_type='text/plain')
        for text in plaintext:
            txtmsg = ""
            txtmsg = text[1].decode()
            logging.info("Body is %s" % txtmsg)

        # Setup a query object.
        query = User.all()
        # Filter the user objects to get only the emails in the CC list.
        query.filter("userEmail IN",  cc_addresses)
        # But, only get at most 10 users.
        users = query.fetch(10)

        logging.info('Got %d user entities from the datastore.' % len(users))

        # Iterate over each of the users increasing their score by one.
        for user in users:
            user.userScore += 1

        # Now, write the users back to the datastore.
        db.put(users)
        logging.info('Wrote %d user entities.' % len(users))

我会对您的模型结构进行调整。当您创建用户实体时，我会将 key_name 设置为电子邮件地址。您将能够使查询更加高效。

一些引用:

• List Comprehension .
• Query Object .
• db.put() .