title: discord.py AttributeError: 'str' object has no attribute 'id'
body: <p>so the thing is, i'm making a discord bot in python with python.py and i'm making a command to mute someone by put their user id in a json file.</p>
  
  <pre><code>@client.command()
  async def mute(user):
  with open("muted.json", 'r') as f:
      data = json.load(f)
  if not user.id in data:
      data[user.id] = {}
  else:
      await client.send_message(message.channel, "The user is already muted")
  </code></pre>
  
  <p>It's saying at "if not user.id in data:" that "AttributeError: 'str' object has no attribute 'id'"
  How can I fix that ?</p>