我在使用discord.py处理错误时遇到了一些问题。我已经设置了以下命令：
class InvalidVoiceChannel(VoiceConnectionError):
"""Exception for cases of invalid Voice Channels."""
@commands.command(name='connect', aliases=['join'])
async def connect_(self, ctx, *, channel: discord.VoiceChannel = None):
if not channel:
try:
channel = ctx.author.voice.channel
except AttributeError:
raise InvalidVoiceChannel(
'No channel to join. Please either specify a valid channel'
' or join one.'
)
vc = ctx.voice_client
if vc:
if vc.channel.id == channel.id:
return
try:
await vc.move_to(channel)
except asyncio.TimeoutError:
raise VoiceConnectionError(
f'Moving to channel: <{channel}> timed out.'
)
else:
try:
await channel.connect()
except asyncio.TimeoutError:
raise VoiceConnectionError(
f'Connecting to channel: <{channel}> timed out.'
)
)
await ctx.send(f'Connected to: **{channel}**', delete_after=20)
运行该程序并将作者连接到语音通道时，一切正常，并且漫游器已连接到该通道。但是，当作者未连接到语音通道（并且未将其作为参数传递）时，错误不会出现出现，并且不会调用错误处理程序（如下）：
async def __error(self, ctx, error):
if isinstance(error, commands.NoPrivateMessage):
try:
return await ctx.send(
'This command can not be used in private messages.'
)
except discord.HTTPException:
pass
elif isinstance(error, InvalidVoiceChannel):
await ctx.send(
'Error connecting to voice channel. Please make sure you are'
' in a valid channel or provide me with one.'
)
else:
raise error
一旦我按下 Ctrl + C 终止了bot，那么我看到了以下内容：
Ignoring exception in command connect:
Traceback (most recent call last):
File "/home/danth/Code/discord-sounds/sounds/cogs/music.py", line 269, in connect_
channel = ctx.author.voice.channel
AttributeError: 'NoneType' object has no attribute 'channel'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/home/danth/Code/.virtualenvs/discord-sounds/lib/python3.7/site-packages/discord/ext/commands/bot.py", line 863, in invoke
await ctx.command.invoke(ctx)
File "/home/danth/Code/.virtualenvs/discord-sounds/lib/python3.7/site-packages/discord/ext/commands/core.py", line 728, in invoke
await injected(*ctx.args, **ctx.kwargs)
File "/home/danth/Code/.virtualenvs/discord-sounds/lib/python3.7/site-packages/discord/ext/commands/core.py", line 79, in wrapped
ret = await coro(*args, **kwargs)
File "/home/danth/Code/discord-sounds/sounds/cogs/music.py", line 272, in connect_
'No channel to join. Please either specify a valid channel'
cogs.music.InvalidVoiceChannel: No channel to join. Please either specify a valid channel or join one.
为什么不调用错误处理程序，为什么不立即显示回溯？