title: Why can't I use command prefixes?
body: <p>Every I try to use the <code>commands.Bot(command_prefix='')</code>, the program reads it as an error. For example, with the code below, it comes out with</p>
  <blockquote>
  <p><em>Ignoring exception in command None: discord.ext.commands.errors.CommandNotFound: Command &quot;-ping&quot; is not
  found Ignoring exception in command None:
  discord.ext.commands.errors.CommandNotFound: Command &quot;ping&quot; is not
  found</em></p>
  </blockquote>
  <p>and is repeated a few times before what i wanted the bot to say (Pong!), is sent 2 or more times in the server...</p>
  <p>\I think it might be looping? I'm not sure, but I got it to work once, but the longer I waited, every time used the command it sent more responses? -it sent 16 'Pong's last time I tried... Is there anything I can do about this?\</p>
  <p>How can i fix this?</p>
  <pre><code>from discord.ext import commands
  client = commands.Bot(command_prefix='-')
  
  @client.event
  async def on_ready():
      print(&quot;Bot is ready for use...&quot;)
  
  @client.command()
  async def ping(ctx):
      await ctx.send('Pong')
  
  client.run('TOKEN')
  </code></pre>