Python .on event triggers
"""
You need to use the Observer Pattern (http://en.wikipedia.org/wiki/Observer_pattern).
In the following code, a person subscribes to receive updates from the global wealth entity.
When there is a change to global wealth, this entity then alerts all
its subscribers (observers) that a change happened. Person then updates itself.
I make use of properties in this example, but they are not necessary.
A small warning: properties work only on new style classes, so
the (object) after the class declarations are mandatory for this to work.
"""
class GlobalWealth(object):
def __init__(self):
self._global_wealth = 10.0
self._observers = []
@property
def global_wealth(self):
return self._global_wealth
@global_wealth.setter
def global_wealth(self, value):
self._global_wealth = value
for callback in self._observers:
print('announcing change')
callback(self._global_wealth)
def bind_to(self, callback):
print('bound')
self._observers.append(callback)
class Person(object):
def __init__(self, data):
self.wealth = 1.0
self.data = data
self.data.bind_to(self.update_how_happy)
self.happiness = self.wealth / self.data.global_wealth
def update_how_happy(self, global_wealth):
self.happiness = self.wealth / global_wealth
if __name__ == '__main__':
data = GlobalWealth()
p = Person(data)
print(p.happiness)
data.global_wealth = 1.0
print(p.happiness)