Call Async Functions Dynamically with exec()

Question

So, I'm implementing a Discord Bot using discord.py, and I'm trying to dynamically call functions based on commands. I was able to test dynamic function calls with exec() fine, but they seem to fall apart with the async calls needed for discord.py.

So what I'm trying to do with this example would be to call the hello function and print Hello World into discord by typing !hello in chat.

@client.event
async def on_message(message):
    call = 'await ' + message.content.lower()[1:] + '(message)'
    exec(call)

async def hello(message):
    await client.send_message(message.channel, 'Hello World')

Unfortunately, this code doesn't seem to do anything, I'm assuming because of how exec() handles async calls. Any help would be appreciated.

Udi · Accepted Answer · 2017-06-24 06:38:23Z

Instead of exec() use globals() to get your function:

import asyncio


async def main():
    s = "foo"
    param = "hello"
    coro = globals().get(s)
    if coro:
        result = await coro(param)
        print("got:", result)
    else:
        print("unknown function:", s)


async def foo(param):
    print(param)
    await asyncio.sleep(0.11)
    return ":-)"


loop = asyncio.get_event_loop()
response = loop.run_until_complete(main())
loop.close()

However, allowing the user to access anything in globals() might bwe dangerous, instead it would be much better to whitelist your commands, for example using:

import asyncio

my_commands = {}


def register(cmd):
    my_commands[cmd.__name__] = cmd
    return cmd


async def main():
    s = "foo"
    param = "hello"
    coro = my_commands.get(s)
    if coro:
        result = await coro(param)
        print("got:", result)
    else:
        print("unknown function:", s)


@register
async def foo(param):
    """I am the mighty foo command!"""
    print(param)
    await asyncio.sleep(0.11)
    return ":-)"



loop = asyncio.get_event_loop()
response = loop.run_until_complete(main())
loop.close()

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