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Responding to Messages
In this lesson, you’ll learn how to make your bot respond to specific messages in a chat. You’ll add on to the previous functionality of your bot by handling the on_message() event.
Because a Client can’t tell the difference between a bot user and a normal user account, your on_message() handler should protect against a potentially recursive case where the bot sends a message that it might handle itself. You’ll learn how to compare the message.author to the client.user (your bot user), and ignore any of its own messages.
00:00 This is part nine, and now you will take a look at how to respond to specific messages in the chat.
00:07
Before your bot begins to respond to specific messages within chat, you must modify your on_message() event handler. The example you can currently see onscreen is a complete example. Before you see how it runs, however, we should delve into it and see what’s going on.
00:23
So let’s start at the top. This first line, if message.author == client.user: is a very important section, even though it’s one line. Two, if you include the return for the if.
00:35
Because the Client is unable to know the difference between a bot user and a regular user account, the on_message() handler should be able to protect against a potentially recursive situation where the bot sends a message that it may, then, handle and respond to.
00:48 That’s what this line achieves. So, what does this mean? Well, let’s have a look at an example where this line would be critical. Let’s say you wanted your bot to respond to somebody saying “Happy Birthday” within your channel.
01:02
That handler could look something along the lines of what this one looks like. What’s it doing? Well, if 'happy birthday' is somewhere within the message sent to
01:13 chat, send to that channel the message “Happy Birthday”. So, apart from being naturally quite spammy, the way it’s implemented here could have a very, very annoying side effect.
01:26
The message that the bot is supposed to handle, i.e. 'happy birthday', is contained within the response of the bot. This means that if one person sends, “Happy Birthday”, then the bot will respond with “Happy Birthday”, which means the bot will then respond with “Happy Birthday”, meaning the bot will then, again, respond with “Happy Birthday”, meaning the bot will respond with “Happy Birthday”, meaning that the bot—see what’s happening?
01:48
This is why checking the author of the message is so important. It means that the bot will ignore its own messages and not respond to them.
01:56 Let’s take a look at this in action. If we run the bot,
02:03 there we go. It’s connected. Now, let’s jump over to Discord.
02:12
There you go. The RealPythonTutorialBot is just replying to itself constantly. It’s taking a breather every now and then, but otherwise, it’s just constantly going and it will continue to go until we stop the bot. Again, this is why checking the author of the message is so important.
02:30 It means that the bot will ignore its own messages and not respond to them.
02:34
While that happy birthday bot is a very specific example, at least now you have an idea of what could go wrong if you don’t check the author of the message.
02:43
So, let’s just make sure that’s there. brooklyn_99_quotes is just a collection of quotes that the bot has to choose from when it responds to the message.
02:55
The final section of the on_message() event handler is this part: if message.content == '99!':. This is what defines the message that your bot will respond to. In other words, it will check every message that is sent within chat to see if it is equal to '99!'. If it’s not, it’ll just wait for the next one.
03:16
If it is, however, it will jump into the if loop. Here it’ll choose a response randomly from the brooklyn_99_quotes variable. Keep in mind, because it is random.choice() you must, at the top of your file, import random.
03:35
Very important. It won’t work if you don’t do that. After choosing a random response, it will then send() that response to the channel where the '99!' message was originally sent.
03:47
Now that we’ve completed delving into the on_message() event handler, let’s run the program, wait for it to connect,
03:57 and head over to Discord to test this functionality. Ignore all the “Happy Birthday” messages, and send “99!”
04:06 There you have it. You have a response from the bot and it’s not constantly going. Awesome job. Now that you’ve seen some ways to handle common Discord events, next up, you will learn how to deal with errors that event handlers may raise.
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