def _initial(self, event):
    'Raises a NotImplementedError to force the derived class\n        to implement its own initial state.\n        '
    raise NotImplementedError
Raises a NotImplementedError to force the derived class
to implement its own initial state.
def _initial(self, event):
    'Raises a NotImplementedError to force the derived class\n        to implement its own initial state.\n        '
    raise NotImplementedError