title: How do i lock a channel that is mentioned? Discord.py
body: <p>Here is my code, It only locks the current channel I'm in, I feel a bit stupid as i think i should know this lol. For example, I want to say '-lock #channelname but it only locks my current channel.</p>
  <pre><code>@client.command()
  @commands.has_permissions(manage_channels=True)
  async def lock(ctx, channel : discord.TextChannel=None):
      overwrite = ctx.channel.overwrites_for(ctx.guild.default_role)
      overwrite.send_messages = False
      await ctx.channel.set_permissions(ctx.guild.default_role, overwrite=overwrite)
      await ctx.send('Channel locked.')
  @lock.error
  async def lock_error(ctx, error):
      if isinstance(error,commands.CheckFailure):
          await ctx.send('You do not have permission to use this command!')
  </code></pre>