Discord.py: MissingRequiredArgument

Created on 15 Feb 2017 · 6Comments · Source: Rapptz/discord.py

When you're missing an argument for a command, instead of calling 'except Exception:', you drop the entire code and display an error that does not return a message into chat.

Example

@bot.command()
async def test(myvar : str):
    'Test command for exceptions'
    try:
        await bot.say(myvar)
    except Exception:
        await bot.say('Proper usage: test string')
        return

Instead, console outputs:

Ignoring exception in command test
Traceback (most recent call last):
File "/usr/local/lib/python3.5/dist-packages/discord/ext/commands/bot.py", line 848, in process_commands
yield from command.invoke(ctx)
File "/usr/local/lib/python3.5/dist-packages/discord/ext/commands/core.py", line 362, in invoke
yield from self.prepare(ctx)
File "/usr/local/lib/python3.5/dist-packages/discord/ext/commands/core.py", line 340, in prepare
yield from self._parse_arguments(ctx)
File "/usr/local/lib/python3.5/dist-packages/discord/ext/commands/core.py", line 299, in _parse_arguments
transformed = yield from self.transform(ctx, param)
File "/usr/local/lib/python3.5/dist-packages/discord/ext/commands/core.py", line 207, in transform
raise MissingRequiredArgument('{0.name} is a required argument that is missing.'.format(param))
discord.ext.commands.errors.MissingRequiredArgument: myvar is a required argument that is missing.

Source

Oricul

Most helpful comment

How do you expect lib to pass a variable into your function if there is no argument provided? Use an error handler and check the error type instead.

A "generic" error handler would be like

@bot.event
async def on_command_error(error, ctx):
    # you can compare error here

A "per-command" error handler would be like

@test.error
async def test_error(error, ctx): 
    ...

Here's the code for error dispatching. And here's the code for "per-command" error handler decorator. And you can find types of errors here.

Helehelehele on 15 Feb 2017

👍7

All 6 comments

The error is correct, an argument is missing, you should catch the error using the event on_command_error to return a message

ghost on 15 Feb 2017

👍4

How do you expect lib to pass a variable into your function if there is no argument provided? Use an error handler and check the error type instead.

A "generic" error handler would be like

@bot.event
async def on_command_error(error, ctx):
    # you can compare error here

A "per-command" error handler would be like

@test.error
async def test_error(error, ctx): 
    ...

Here's the code for error dispatching. And here's the code for "per-command" error handler decorator. And you can find types of errors here.

Helehelehele on 15 Feb 2017

👍7

My understanding is that if it couldn't fulfill try then it would process except, but I've been coding in Python for a whole day - so forgive my lack of understanding.
I did search and find the bot.py, but really couldn't understand it very well - I even went as far as adding 'except on_command_error', but apparently I did not make it far enough.

Thanks for the code snippit, Helehelehele.

I apologize for opening an issue.

Oricul on 15 Feb 2017

😕3 👍2

Could someone provide an example of the original code of using the on_command_error function?