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Chain of responsibility in python (Design Patterns - Gamma, Helm, Johnson, Vlissides)
PRINT_TOPIC = 1
PAPER_ORIENTATION = 2
APPLICATION_TOPIC = 3
NO_HELP_TOPIC = -1
class HelpHandler (object):
def __init__(self, successor=0, topic=NO_HELP_TOPIC):
self._successor = successor
self._topic = topic
def HasHelp(self):
return self._topic != NO_HELP_TOPIC;
def HandleHelp(self):
if self._successor != 0:
self._successor.HandleHelp()
def SetHandler(self,h,t):
self._successor = h
self._h = t
class Widget(HelpHandler):
def __init__(self, w, t):
super(Widget,self).__init__(w,t)
class Button(Widget):
def __init__(self, d, t):
super(Button,self).__init__(d,t)
def HandleHelp(self):
if self.HasHelp():
print "Button Help"
else:
return super(Button, self).HandleHelp()
class Dialog(Widget):
def __init__(self, h, t):
super(Dialog,self).__init__(h,t)
self.SetHandler(h,t)
def HandleHelp(self):
if self.HasHelp():
print "Dialog Help"
else:
return super(Dialog, self).HandleHelp()
class Application(HelpHandler):
def __init__(self, t):
super(Application,self).__init__(0,t)
def HandleHelp(self):
print "Application Help"
def main():
application = Application(APPLICATION_TOPIC)
dialog = Dialog(application, PRINT_TOPIC)
button = Button(dialog, NO_HELP_TOPIC)
# invoking help in the chain
button.HandleHelp()
if __name__ == "__main__":
main()
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