3. Hello, world!

On the homepage, we showed you the following "Hello world!" plugin as an example:

from errbot import BotPlugin, botcmd

class HelloWorld(BotPlugin):
    """Example 'Hello, world!' plugin for Errbot"""

    @botcmd
    def hello(self, msg, args):
        """Say hello to the world"""
        return "Hello, world!"

In this chapter, you will learn exactly how this plugin works.

I will assume you've configured the BOT_EXTRA_PLUGIN_DIR as described in the previous chapter. To get started, create a new, empty directory named HelloWorld inside this directory.

Create a new file called helloworld.py inside the HelloWorld directory you just created. This file contains all the logic for your plugin, so copy and paste the above example code into it.

3.1. Anatomy of a BotPlugin

Although this plugin is only 9 lines long, there is already a lot of interesting stuff going on here. Lets go through it step by step.

from errbot import BotPlugin, botcmd

This should be pretty self-explanatory. Here we import the BotPlugin class and the botcmd() decorator. These let us build a class that can be loaded as a plugin and allow us to mark methods of that class as bot commands.

class HelloWorld(BotPlugin):
    """Example 'Hello, world!' plugin for Errbot"""

Here we define the class that makes up our plugin. The name of your class, HelloWorld in this case, is what will make up the name of your plugin. This name will be used in commands such as !status, !plugin load and !plugin unload

The class' docstring is used to automatically populate the built-in command documentation. It will be visible when issuing the !help command.

Warning

A plugin should only ever contain a single class inheriting from BotPlugin

@botcmd
def hello(self, msg, args):
    """Say hello to the world"""
    return "Hello, world!"

This method, hello, is turned into a bot command which can be executed because it is decorated with the botcmd() decorator. Just as with the class docstring above, the docstring here is used to populate the !help command.

The name of the method, hello in this case, will be used as the name of the command. That means this method creates the !hello command.

Note

The method name must comply with the usual Python naming conventions for identifiers , that is, they may not begin with a digit (like 911 but only with a letter or underscore, so _911 would work) and cannot be any of the reserved keywords such as pass (instead use password) etc.

Note

Should multiple plugins define the same command, they will be dynamically renamed (by prefixing them with the plugin name) so that they no longer clash with each other.

If we look at the function definition, we see it takes two parameters, msg and args. The first is a Message object, which represents the full message object received by Errbot. The second is a string (or a list, if using the split_args_with parameter of botcmd()) with the arguments passed to the command.

For example, if a user were to say !hello Mister Errbot, args would be the string "Mister Errbot".

Finally, you can see we return with the string Hello, world!. This defines the response that Errbot should give. In this case, it makes all executions of the !hello command return the message Hello, world!.

Note

If you return None, Errbot will not respond with any kind of message when executing the command.

3.2. Plugin metadata

We have our plugin itself ready, but if you start the bot now, you'll see it still won't load your plugin. What gives?

As it turns out, you need to supply a file with some meta-data alongside your actual plugin file. This is a file that ends with the extension .plug and it is used by Errbot to identify and load plugins.

Lets go ahead and create ours. Place the following in a file called helloworld.plug:

[Core]
Name = HelloWorld
Module = helloworld

[Python]
Version = 2+

[Documentation]
Description = Example "Hello, world!" plugin

Note

This INI-style file is parsed using the Python configparser class. Make sure to use a valid file structure.

Lets look at what this does. We see two sections, [Core] , and [Documentation]. The [Core] section is what tells Errbot where it can actually find the code for this plugin.

The key Module should point to a module that Python can find and import. Typically, this is the name of the file you placed your code in with the .py suffix removed.

The key Name should be identical to the name you gave to the class in your plugin file, which in our case was HelloWorld. While these names can differ, doing so is not recommended.

Note

If you're wondering why you have to specify it when it should be the same as the class name anyway, this has to do with technical limitations that we won't go into here.

The [Documentation] section will be explained in more detail further on in this guide, but you should make sure to at least have the Description item here with a short description of your plugin.

3.3. Wrapping up

If you've followed along so far, you should now have a working Hello, world! plugin for Errbot. If you start your bot, it should load your plugin automatically.

You can verify this by giving the !status command, which should respond with something like the following:

Yes I am alive...
With these plugins (A=Activated, D=Deactivated, B=Blacklisted, C=Needs to be configured):
[A] ChatRoom
[A] HelloWorld
[A] VersionChecker
[A] Webserver

If you don't see your plugin listed or it shows up as unloaded, make sure to start your bot with DEBUG-level logging enabled and pay close attention to what it reports. You will most likely see an error being reported somewhere along the way while Errbot starts up.

3.4. Next steps

You now know enough to create very simple plugins, but we have barely scratched the surface of what Errbot can do. The rest of this guide will be a recipe-style set of topics that cover all the advanced features Errbot has to offer.