如何在discord.py欢迎信息中使用ctx？

import discord
from discord.ext import commands

intents = discord.Intents.default()
intents.members = True

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

@bot.event
async def on_member_join(member):
    guild = member.guild
    welcome_channel = discord.utils.get(guild.channels, name="welcome") # 欢迎频道名称，请根据实际情况修改

    # 使用ctx获取相关信息
    ctx = await bot.get_context(member.message)
    server_name = ctx.guild.name
    member_count = len(ctx.guild.members)

    # 构建欢迎信息
    welcome_message = f"欢迎 {member.mention} 加入 {server_name}！当前服务器成员数：{member_count}人。"

    # 发送欢迎信息
    await welcome_channel.send(welcome_message)

bot.run('YOUR_BOT_TOKEN')