Cogs

There comes a point in your bot’s development when you want to organize a collection of commands, listeners, and some state into one class. Cogs allow you to do just that.

The gist:

• Each cog is a Python class that subclasses Cog.

• Every command is marked with the discord.command() decorator or the corresponding shortcut command decorator.

• Every listener is marked with the Cog.listener() decorator.

• Cogs are then registered with the Bot.add_cog() call.

• Cogs are subsequently removed with the Bot.remove_cog() call.

Quick Example

This example cog defines a Greetings category for your commands, with a single slash command named hello as well as a listener to listen to an Event.

class Greetings(discord.Cog):
    def __init__(self, bot):
        self.bot = bot
        self._last_member = None

    @discord.Cog.listener()
    async def on_member_join(self, member):
        channel = member.guild.system_channel
        if channel is not None:
            await channel.send(f'Welcome {member.mention}.')

    @discord.slash_command()
    async def hello(self, ctx, *, member: discord.Member = None):
        """Says hello"""
        member = member or ctx.author
        if self._last_member is None or self._last_member.id != member.id:
            await ctx.send(f'Hello {member.name}~')
        else:
            await ctx.send(f'Hello {member.name}... This feels familiar.')
        self._last_member = member

A couple of technical notes to take into consideration:

• All listeners must be explicitly marked via decorator, listener().

• The name of the cog is automatically derived from the class name but can be overridden.

• All commands must now take a self parameter to allow usage of instance attributes that can be used to maintain state.

Cog Registration

Once you have defined your cogs, you need to tell the bot to register the cogs to be used. We do this via the add_cog() method.

bot.add_cog(Greetings(bot))

This binds the cog to the bot, adding all commands and listeners to the bot automatically.

Using Cogs

Just as we remove a cog by its name, we can also retrieve it by its name as well. This allows us to use a cog as an inter-command communication protocol to share data. For example:

class Economy(discord.Cog):
    ...

    async def withdraw_money(self, member, money):
        # implementation here
        ...

    async def deposit_money(self, member, money):
        # implementation here
        ...

class Gambling(discord.Cog):
    def __init__(self, bot):
        self.bot = bot

    def coinflip(self):
        return random.randint(0, 1)

    @discord.slash_command()
    async def gamble(self, ctx, money: int):
        """Gambles some money."""
        economy = self.bot.get_cog('Economy')
        if economy is not None:
            await economy.withdraw_money(ctx.author, money)
            if self.coinflip() == 1:
                await economy.deposit_money(ctx.author, money * 1.5)