在树莓派上播放python discordbot无效

Question

import asyncio

import discord
from discord.ext import commands
from discord.utils import get
import youtube_dl
import os

TOKEN = '****'
BOT_PREFIX = '-'

bot = commands.Bot(command_prefix=BOT_PREFIX)


@bot.event
async def on_ready():
    print('Logged in as {}'.format(bot.user.name))
    bot.loop.create_task(status_task())


async def status_task():
    while True:
        await bot.change_presence(activity=discord.Game('just vibing'), status=discord.Status.online)
        await asyncio.sleep(3)
        await bot.change_presence(activity=discord.Game('just a bot being a bot'), status=discord.Status.online)
        await asyncio.sleep(3)


@bot.command(pass_context=True, aliases=['j', 'come',])
async def join(ctx):
    global voice
    channel = ctx.message.author.voice.channel
    voice = get(bot.voice_clients, guild=ctx.guild)
    
    if voice and voice.is_connected():
        await voice.move_to(channel)
    else:
        voice = await channel.connect()
    
    await voice.disconnect
    
    if voice and voice.is_connected():
        await voice.move_to(channel)
    else:
        voice = await channel.connect()
        print(f"The bot has connect to {channel}\n")
        
    await ctx.send(f"Joined{channel}")
    
@bot.command(pass_context=True, aliases=['l', 'piss',])
async def leave(ctx):
    channel = ctx.message.author.voice.channel
    voice = get(bot.voice_clients, guild=ctx.guild)

    if voice and voice.is_connected():
        await voice.disconnect()
        print(f"The bot has left {channel}")
        await ctx.send(f"Left {channel}")
    else:
        print("Bot was told to leave voice channel, but was not in one")
        await ctx.send("Don't thin I am in a voice channel")
        
@bot.command(pass_context=True, aliases=['p', 'pla'])
async def play(ctx, url: str):

    song_there = os.path.isfile("song.mp3")
    try:
        if song_there:
            os.remove("song.mp3")
            print("Removed old song file")
    except PermissionError:
        print("Trying to delete song file, but it's being played")
        await ctx.send("ERROR: Music playing")
        return

    await ctx.send("Getting everything ready now")

    voice = get(bot.voice_clients, guild=ctx.guild)

    ydl_opts = {
        'format': 'bestaudio/best',
        'postprocessors': [{
            'key': 'FFmpegExtractAudio',
            'preferredcodec': 'mp3',
            'preferredquality': '192',
        }],
    }

    with youtube_dl.YoutubeDL(ydl_opts) as ydl:
        print("Downloading audio now\n")
        ydl.download([url])

    for file in os.listdir("./"):
        if file.endswith(".mp3"):
            name = file
            print(f"Renamed File: {file}\n")
            os.rename(file, "song.mp3")

    voice.play(discord.FFmpegPCMAudio("song.mp3"), after=lambda e: print("Song done!"))
    voice.source = discord.PCMVolumeTransformer(voice.source)
    voice.source.volume = 0.07

    nname = name.rsplit("-", 2)
    await ctx.send(f"Playing: {nname[0]}")
    print("playing\n")
    
        
    
bot.run(TOKEN)

我用python 3.6.10在树莓派上制作了一个discord机器人，但play命令不起作用。 join和leave命令工作正常。我也尝试了一个新的python版本，但是它也不起作用。这是带有Raspbian OS Lite的RaspberryPi 2B。我想-play youtubeurl ，然后应该将youtubevideo下载为mp3文件并将其重命名为song.mp3。我认为这有效。但是，当它应该播放mp3文件时，就会出现很多错误，而且我不知道如何解决。 错误：

Ignoring exception in command play:
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/discord/ext/commands/core.py", line 85, in wrapped
    ret = await coro(*args, **kwargs)
  File "bot.py", line 99, in play
    voice.play(discord.FFmpegPCMAudio("song.mp3"), after=lambda e: print("Song done!"))
AttributeError: 'NoneType' object has no attribute 'play'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/discord/ext/commands/bot.py", line 903, in invoke
    await ctx.command.invoke(ctx)
  File "/usr/local/lib/python3.6/site-packages/discord/ext/commands/core.py", line 859, in invoke
    await injected(*ctx.args, **ctx.kwargs)
  File "/usr/local/lib/python3.6/site-packages/discord/ext/commands/core.py", line 94, in wrapped
    raise CommandInvokeError(exc) from exc
discord.ext.commands.errors.CommandInvokeError: Command raised an exception: AttributeError: 'NoneType' object has no attribute 'play'