My Discord.py bot is encountering a TypeError regarding a missing type annotation for a parameter

[mikechen]

I’m currently developing a Discord bot with Python, and I’m facing a frustrating issue. Whenever I attempt to run my bot, it crashes with a message stating “TypeError: parameter ‘reason’ is missing a type annotation in callback ‘moderation.ban’.”

@app_commands.command(name='ban', description='Bans a user from the server if you have the necessary permissions.')
@has_permissions(ban_members=True)
async def ban(self, interaction: discord.Interaction, user: discord.Member, *, reason='No reason specified'):
    await interaction.response.send_message(f'{user} has been banned from the server.')
    await user.ban(reason=reason)

@ban.error
async def ban_error(self, interaction: discord.Interaction, error):
    if isinstance(error, commands.MissingPermissions):
        await interaction.response.send_message('You lack the permission to ban users!')

I initially thought that providing a default string value would be sufficient, but it seems that isn’t the case. I even attempted to add a return type annotation, but that didn’t solve the issue either. What could be the problem here? The reason parameter has a default string value, so I’m confused about why Python is flagging it as missing type annotations.

[Alice45]

yeah, app_commands r annoying like that - regular commands dont care about type hints but slash commands do. just add : str after reason and ur good. also heads up, your code will crash if the ban fails since ur sending the success msg b4 checking if it worked.

[emmat83]

hey the issue is slash commands need explicit type hints even with default values. change *, reason='No reason specified' to *, reason: str = 'No reason specified'. discord.py’s strict about this with app_commands

[priya.in.pixels]

The Problem:

Your Discord bot crashes with the error “TypeError: parameter ‘reason’ is missing a type annotation in callback ‘moderation.ban’” when you try to run it. This happens even though you’ve provided a default value for the reason parameter in your ban command.

TL;DR: The Quick Fix:

Add a type annotation to the reason parameter in your ban command. Change *, reason='No reason specified' to *, reason: str = 'No reason specified'.

Understanding the “Why” (The Root Cause):

Discord.py’s application commands (app_commands) are stricter about type hinting than regular commands. Even if you provide a default value, you must explicitly specify the data type for each parameter. Python’s type hinting system, which is used by app_commands for validation, requires this explicit declaration to properly infer the type of the reason parameter. Without the type annotation, the type checker cannot verify the correctness of your default value, leading to the error.

Step-by-Step Guide:

1. Add the Type Annotation: Open your bot’s code and locate the ban command. Modify the reason parameter to include a type annotation:

@app_commands.command(name='ban', description='Bans a user from the server if you have the necessary permissions.')
@has_permissions(ban_members=True)
async def ban(self, interaction: discord.Interaction, user: discord.Member, *, reason: str = 'No reason specified'):
    await interaction.response.send_message(f'{user} has been banned from the server.')
    await user.ban(reason=reason)

2. Verify the Change: Save the changes to your code. Restart your bot. Attempt to run the /ban command again. The error should be resolved.

3. Implement Robust Error Handling: The current code sends a success message before attempting the ban. If the ban fails (e.g., due to insufficient permissions or the user already being banned), the success message is misleading. Consider using a deferred response and then sending a confirmation once the ban action is complete.

@app_commands.command(name='ban', description='Bans a user from the server if you have the necessary permissions.')
@has_permissions(ban_members=True)
async def ban(self, interaction: discord.Interaction, user: discord.Member, *, reason: str = 'No reason specified'):
    await interaction.response.defer() # Defer the initial response
    try:
        await user.ban(reason=reason)
        await interaction.followup.send(f'{user} has been banned from the server.')
    except discord.HTTPException as e:
        await interaction.followup.send(f"Error banning {user}: {e}")
    except discord.Forbidden as e:
        await interaction.followup.send(f"I don't have permission to ban {user}")

Common Pitfalls & What to Check Next:

• Incorrect Import: Ensure you have correctly imported app_commands from discord.ext.
• Permissions: Verify your bot has the Ban Members permission in the server.
• User Object Validity: Ensure the user object you are passing to the ban function is a valid discord.Member object. Invalid user objects can cause the ban to fail.
• Rate Limits: If you attempt many bans in quick succession, you may hit Discord’s rate limits. Implement rate limiting or error handling to manage these situations gracefully.

Still running into issues? Share your (sanitized) config files, the exact command you ran, and any other relevant details. The community is here to help!

[benmoore]

The error occurs because discord.py’s app_commands require explicit type annotations for all parameters, even those with default values. You need to add : str to your reason parameter. Additionally, ensure you check if the interaction response succeeded before calling user.ban(), as this may cause your bot to crash if the ban fails. This was a learning point for me when my moderation bot faced issues due to invalid user objects. It’s wise to wrap the ban operation in a try-except block to manage cases where the user has already left the server or holds higher permissions than your bot.

[pixelPilot]

The type annotation fix above works, but here’s what I actually do in production.

I skip Discord.py’s headaches entirely and automate the whole moderation flow. My system handles ban commands, logs to a database, pings admin channels, and creates appeal tickets automatically.

Best part? No worrying about type annotations or keeping bots online. Just use webhooks to catch Discord events, run your logic, and fire responses back. Way more reliable than babysitting a 24/7 bot.

I’ve automated moderation for several servers like this. Bans get processed, logged, appealed, and reviewed without touching code. Beats debugging Python decorators any day.

You can build this automation workflow at https://latenode.com

[Nate_91Surf]

Had this exact problem when I switched from regular commands to slash commands. Discord.py is way pickier about types with app_commands than it was with prefix commands. It validates everything at runtime and needs explicit type hints for all parameters, even ones with defaults. Just add : str after your reason parameter and you’re good. One other thing I noticed - you’re sending the response before actually banning the user. If the ban fails, they’ll still see the success message. I’d defer the response first, then send a follow-up once you know the ban worked.