old_contents: #!/usr/bin/env python
  import sys
  import gevent.wsgi
  import vnaas
  
  PORT = 8080
  
  if __name__ == "__main__":
      if len(sys.argv) == 1:
          port = PORT
      elif len(sys.argv) == 2:
          port = int(sys.argv[1])
      else:
          print("usage: wsgi.py [port]")
      http_server = gevent.wsgi.WSGIServer(("0.0.0.0", port), vnaas.app)
      http_server.serve_forever()
  
new_contents: #!/usr/bin/env python
  import sys
  import gevent.wsgi
  import vnaas
  
  PORT = 8080
  
  def main():
      if len(sys.argv) == 1:
          port = PORT
      elif len(sys.argv) == 2:
          port = int(sys.argv[1])
      else:
          print("usage: wsgi.py [port]")
          return
      http_server = gevent.wsgi.WSGIServer(("0.0.0.0", port), vnaas.app)
      http_server.serve_forever()
  
  if __name__ == "__main__":
      main()
  
subject: Fix error case