> I think that Your trace_returns function is actually a global trace > that returns itself and does not handle the 'call' event.
By returning itself, the global trace also becomes the local trace. The code in bdb.py does the same thing--- self.trace_dispatch is set as the global trace, and returns self.trace_dispatch via self.dispatch_call(frame, arg) -- http://mail.python.org/mailman/listinfo/python-list
