Print to `stream` the event handlers installed for this flow.

def show_event_handlers(self, stream=sys.stdout, verbose=0):
        """Print to `stream` the event handlers installed for this flow."""
        lines = ["List of event handlers installed:"]
        for handler in self.event_handlers:
            if verbose:
                lines.extend(handler.__class__.cls2str().split("\n"))
            else:
                lines.extend(str(handler).split("\n"))

        stream.write("\n".join(lines))
        stream.write("\n")