I am writing a bot for Discord in Python (discordbot.py 0.2.3a3). I need a bot to play music.

```
import asyncio
import discord
from discord.ext import commands
from discord.ext.commands import bot
bot = commands.Bot(command_prefix='!')
from discord.utils import get
songs = asyncio.Queue()
play_next_song = asyncio.Event()

async def audio_player_task():
    while True:
        play_next_song.clear()
        current = await songs.get()
        current.start()
        await play_next_song.wait()

def toggle_next():
    bot.loop.call_soon_threadsafe(play_next_song.set)

@bot.command(pass_context=True)
async def play(ctx, url):
    if not bot.voice_clients(ctx.message.guild):
        voice = await bot.join_voice_channel(ctx.message.author.voice_channel)
    else:
       voice = bot.voice_client_in(ctx.message.guild)

    player = await voice.create_ytdl_player(url, after=toggle_next)
    await songs.put(player)

bot.loop.create_task(audio_player_task())

```

When I try to play music, I get the following error on line 25 of the code above:

```
discord.ext.commands.errors.CommandInvokeError: Command raised an exception:

TypeError: 'list' object is not callable

```