property puzzle

[Jean Brouwers]

Also, property needs bound methods to get, set, and delete, like

    status = property(self._get_status, self._set_status)

/Jean Brouwers


In article <78b6a744.0408260846.5dc5a0cf at posting.google.com>, george
young <gry at ll.mit.edu> wrote:

> [python 2.3.3, x86 linux, part of a substantial gtk/postgres app]
> I want a Run instance to have a Status instance which inherits
> from Observable. I want to be able to say:
>  
>     thisrun.status = 'planned'
> 
> and have thisrun's _set_status do side-effects and then the status
> object's setter incorporate the new value as it's new state.
> But the setter functions never seem to get called. 
> Am I using "property" wrong?
> 
> class Observable:              #("observer" software pattern)
>     def __init__(self):
>         self.observers = []
>     def register(self, func, *args, **kw):
>         self.observers.append((func, args, kw))
>     def notify(self):
>         for func, args, kw in self.observers: func(*args, **kw)
> 
> class RunStatus(Observable):
>      def __init__(self, val):
>          Observable.__init__(self)
>          self._value = val
>      def set(self, newval):
>          print 'RunStatus.set'
>          self._value = newval
>          self.notify()
>      def get(self):
>          print 'RunStatus.get'
>          return self._value
>     
> class Run:
>     def __init__(self):
>         self._status = RunStatus('planned')
>     def _get_status(self):
>         return self._status
>     def _set_status(self, val):
>         # do various things with val...
>         self._status.set(val)
>     status = property(_get_status, _set_status)
>     
> if __name__ == '__main__':
>     def stat_display():
>         print 'display to screen: r.status=', r.status
>     r = Run()
>     r.status.register(stat_display) #many registers in real app.
>     r.status='hold'
>     print 'status=', r.status
>     print r._status.observers
> 
> Status needs to be a real and persistant object so it's
> observers persist, but needs it's value changed simply, like
>    r.status = 'something'
> 
> [flames about using string values for what is semantically a
>  six valued enum *are* welcome in a separate thread...]