def test_callcapture(self): 

       def func(x, y): 

           print x

           print >>py.std.sys.stderr, y

           return 42

->     res, out, err = py.io.StdCaptureFD.call(func, 3, y=4) 

       assert res == 42 

       assert out.startswith("3") 

       assert err.startswith("4")