andy80@noteboontu:~/documenti/sviluppo/python/twisted_test$ python tw_test1.py 
Ricevuto 45
Ricevuto 46
Unhandled error in Deferred:
Traceback (most recent call last):
  File "tw_test1.py", line 14, in <module>
    d.callback(45)
  File "/usr/lib/python2.5/site-packages/twisted/internet/defer.py", line 239, in callback
    self._startRunCallbacks(result)
  File "/usr/lib/python2.5/site-packages/twisted/internet/defer.py", line 304, in _startRunCallbacks
    self._runCallbacks()
--- <exception caught here> ---
  File "/usr/lib/python2.5/site-packages/twisted/internet/defer.py", line 317, in _runCallbacks
    self.result = callback(self.result, *args, **kw)
  File "tw_test1.py", line 10, in callback_2
    return arg + "ciao"
exceptions.TypeError: unsupported operand type(s) for +: 'int' and 'str'