Thank you very much.
I meant, i cannot test, whether two QStrings are equal with 
"==". For example
  s = QString('hallo')
  t = QString('hallo')
  if s == t: print 'equal1'
  else: print 'not equal1'
  if str(s) == str(t): print 'equal2'
  else: print 'not equal2'
will print out 
  not equal1
  equal2
Sorry for the wrong qauestion.
J.B.