如何检查Discord.py机器人是否已经接入语音通道？

import discord
from discord.ext import commands

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

@bot.command()
async def join(ctx):
    channel = ctx.author.voice.channel
    voice_client = discord.utils.get(bot.voice_clients, guild=ctx.guild)
    
    if voice_client and voice_client.is_connected():
        await ctx.send("机器人已经接入语音通道。")
    else:
        await channel.connect()
        await ctx.send("机器人成功接入语音通道。")

@bot.command()
async def leave(ctx):
    voice_client = discord.utils.get(bot.voice_clients, guild=ctx.guild)
    
    if voice_client and voice_client.is_connected():
        await voice_client.disconnect()
        await ctx.send("机器人已经离开语音通道。")
    else:
        await ctx.send("机器人未连接到语音通道。")

bot.run('YOUR_BOT_TOKEN')