I realise this question has to do with event-handling and i've read about Python event-handler a dispatchers, so either it did not answer my question or i completely missed out the information.
I want method m()
of object A
to be triggered whenever value v
is changing:
For instance (assuming money makes happy):
global_wealth = 0
class Person()
def __init__(self):
self.wealth = 0
global global_wealth
# here is where attribute should be
# bound to changes in 'global_wealth'
self.happiness = bind_to(global_wealth, how_happy)
def how_happy(self, global_wealth):
return self.wealth / global_wealth
So whenever the global_wealth
value is changed, all instances of the class Person
should change their happiness
value accordingly.
NB: I had to edit the question since the first version seemed to suggest i needed getter and setter methods. Sorry for the confusion.
You need to use the 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)