Playing with exceptions through inherited methods.

grandfather clause

"""
Proof of Concept

Following the course of an exception in a class hierarchy similar to that
in Django views.

@author Matthew Purdon

"""


class Parent(object):
	def dispatch(self, method, value):
		handler_name = 'handle_{}'.format(method)
		handler = getattr(self, handler_name)
		print 'Dispatching handler {}'.format(handler_name)
		return handler(value)


class Child(Parent):
	class BadValueException(ValueError):
		def __init__(self, value, *args, **kwargs):
			self.value = value
			super(Child.BadValueException, self).__init__(*args, **kwargs)

	def dispatch(self, method, value):
		try:
			print 'Dispatching from child'
			return super(Child, self).dispatch(method, value)
		except self.BadValueException as error:
			print 'Exception caught: {}'.format(str(error))

	def raises_exception(self, value):
		print 'Raising exception for {}'.format(value)
		raise self.BadValueException(value, 'Bad value "{}" passed in'.format(value))


class GrandChild(Child):
	def handle_int(self, value):
		print 'Handling value {}'.format(value)
		return self.raises_exception(value)

	def handle_float(self, value):
		print 'Converted {} to {}'.format(value, float(value))


if __name__ == "__main__":
 	thing = GrandChild()
 	thing.dispatch('int', 'a')