title: python error-can only join an iterable
body: <p>I am making a program in pygame and I am trying to create with buttons where the user can enter their name. So basically when ever they click on the letter, then it puts that letter into a list. I recreated with about the same variables as in my game and got the same error. So if we can fix this, then I can fix my game. I am using functions so that is why you see the global thing as that is needed. Here is the code. I have looked at other forums btw but nothing that is the same as mine.  </p>
  
  <pre><code>import glob
  unknown=[]
  def bob():
      global unknown
      a=('a').upper()
      unknown=unknown.extend(a)
      unknown=','.join(unknown)
  bob()
  </code></pre>
  
  <p>Again, this is basically what is in my code except for the name of the function and the name of the list, other than that it is the same. The name doesn't matter though. Thanks in advance. </p>