Discord等级系统报错：TypeError: on_message()缺少必填参数'ctx'

Let's break down what's causing this error and fix your level system step by step:

1. The Core Issue: Incorrect Event Listener Setup #

Your on_message method in the Levels cog is missing the required decorator and has an incorrect parameter signature. In Discord.py cogs, event listeners need to be marked with @commands.Cog.listener(), and the on_message event only takes self and message as parameters (no ctx here). Discord.py was throwing the error because it couldn't match the expected argument structure.

2. Broken Command Decorator #

When defining commands inside a cog, you can't use @client.command() — you need to use @commands.command() instead. Cogs rely on the commands module's decorators to properly bind to the bot instance, so using the client-level decorator breaks the cog's functionality.

3. Other Minor Bugs to Fix #

• In your level command, you're checking if member.id exists in self.users, but your JSON stores IDs as strings. You need to convert member.id to a string for the check to work.
• Your embed has two fields both named "Level" — change the second one to "EXP" or "Experience" to avoid confusion.
• Added a safety check for missing users.json files to prevent startup crashes.
• Reduced the save interval from 5 seconds to 5 minutes to avoid excessive disk writes (a more reasonable frequency for data persistence).

Corrected Full Code #

import discord
import asyncio
import json
from discord.ext import commands

class Levels(commands.Cog):  # Inherit from commands.Cog for proper cog functionality
    def __init__(self, client):
        self.bot = client
        self.bot.loop.create_task(self.save_users())
        # Handle missing JSON file gracefully
        try:
            with open(r'C:\Users\conex_000\PycharmProjects\Shirochka\users.json', 'r') as f:
                self.users = json.load(f)
        except FileNotFoundError:
            self.users = {}

    async def save_users(self):
        await self.bot.wait_until_ready()
        while not self.bot.is_closed():
            with open(r'C:\Users\conex_000\PycharmProjects\Shirochka\users.json', 'w') as f:
                json.dump(self.users, f, indent=4)
            await asyncio.sleep(300)  # Save every 5 minutes instead of 5 seconds

    def lvl_up(self, author_id):
        cur_xp = self.users[author_id]['exp']
        cur_lvl = self.users[author_id]['level']
        required_xp = round((4 * (cur_lvl ** 3)) / 5)
        if cur_xp >= required_xp:
            self.users[author_id]['level'] += 1
            # Reset XP to the amount over the required threshold (optional but cleaner)
            self.users[author_id]['exp'] = cur_xp - required_xp
            return True
        else:
            return False

    @commands.Cog.listener()  # Mandatory decorator for cog event listeners
    async def on_message(self, message):
        if message.author == self.bot.user:
            return
        author_id = str(message.author.id)
        if author_id not in self.users:
            self.users[author_id] = {
                'level': 1,
                'exp': 0
            }
        self.users[author_id]['exp'] += 1
        if self.lvl_up(author_id):
            await message.channel.send(f"{message.author.mention} is now level {self.users[author_id]['level']}! 🎉")

    @commands.command(name="level")  # Use commands.command() for cog commands
    async def level_command(self, ctx, member: discord.Member = None):
        member = ctx.author if not member else member
        member_id = str(member.id)
        if member_id not in self.users:
            await ctx.send("This user hasn't sent any messages yet!")
        else:
            embed = discord.Embed(color=member.color, timestamp=ctx.message.created_at)
            embed.set_author(name=f'Level Info - {member.display_name}', icon_url=member.avatar.url)
            embed.add_field(name='Level', value=self.users[member_id]['level'], inline=True)
            embed.add_field(name='EXP', value=self.users[member_id]['exp'], inline=True)
            # Optional: Add progress to next level
            required_xp = round((4 * (self.users[member_id]['level'] ** 3)) / 5)
            embed.add_field(name='To Next Level', value=f"{self.users[member_id]['exp']}/{required_xp}", inline=False)
            await ctx.send(embed=embed)

# Don't forget to load the cog in your main bot code!
# Example:
# client = commands.Bot(command_prefix="!", intents=discord.Intents.all())
# client.add_cog(Levels(client))
# client.run("YOUR_BOT_TOKEN")

Key Improvements Added #

• Added error handling for missing users.json files to prevent startup crashes
• Reduced save frequency to avoid unnecessary disk wear
• Improved the level-up logic to reset XP after leveling up (cleaner progression)
• Enhanced the embed to show the user's avatar and progress to the next level
• Renamed the command method to avoid name conflicts with the class itself

After making these changes, restart your bot, send a few messages, and you should see the level-up messages work correctly. The !level command will also display the user's level and experience properly.

内容的提问来源于stack exchange，提问作者Clonexy