<|im_start|>system
You are a helpful AI assistant.<|im_end|>
<|im_start|>user
Can you write a simple Discord Bot in python that replies with hello world?<|im_end|>
<|im_start|>assistant
Yes, here is a simple code snippet that creates a Discord bot in Python and makes it reply with "Hello, world!" in response to any message:

```python
import discord

client = discord.Client()

@client.event
async def on_ready():
    print('Logged in as {0.user}'.format(client))

@client.event
async def on_message(message):
    if message.author == client.user:
        return

    if message.content.startswith('!hello'):
        await message.channel.send('Hello, world!')

client.run('your_bot_token_here')
```

You will need to replace "your_bot_token_here" with your own Discord bot token. You can obtain a bot token by creating a new bot application on the Discord Developer Portal.<|im_end|>
<|im_start|>user
Instead of hello world, modify the code so that the Discord Bot says hello to the user that messaged it, using their username but not their discord tag.<|im_end|>
<|im_start|>assistant
Sure, here's the modified code that will greet the user by their username:

```python
import discord
from discord.ext import commands

bot = commands.Bot(command_prefix='!')

@bot.command()
async def hello(ctx):
    user = ctx.author
    await ctx.send(f'Hello {user.name}!')

bot.run('YOUR_BOT_TOKEN_HERE')
```

In this modified code, we're using the `ctx.author` attribute to get the user who sent the message, and then using their `name` attribute to greet them by their username.

Save the file and run it in your terminal using `python your_file_name.py`.

Now, when a user types `!hello` in a Discord server where your bot is present, it will reply with "Hello [username]!", where [username] is the username of the user who sent the message.<|im_end|>