title: Error with function returning string
body: <p>I need help with a cryptic error message with python:</p>
  
  <pre><code>def format1(arg1,arg2,arg3,bf):
      yu = 0
      if(bf):
          yu = concat(concat("Back: [",numtostr(arg1)),concat("]: ",concat(arg2,concat(" -- ",arg3))))
      else:
          yu = concat(concat("Forward: [",numtostr(arg1),concat("]: ",concat(arg2,concat(" -- ",arg3))))
      return yu
  </code></pre>
  
  <p>result:</p>
  
  <pre><code>  File "testdirectoryscroll2.py", line 27
      return yu
           ^
  </code></pre>
  
  <p>??? :D</p>