[Python-Dev] Oberver Pattern

[holger krekel]

Raymond Hettinger wrote:
> I would like to know what you all think about formalizing an observer
> protocol for python objects.
> 
> A possible implementation would add Py_TPFLAGS_OBSERVABLE and a slot,
> tp_observer, with a function, PyObject_GenericAttach which registers a
> callable to be notified when the object updates.
> 
> Another approach would be to keep a single registry list with access
> functions:  attach(subject,observer), detach(subject,observer), and
> notifyall(subject).  PyObject_HEAD would have a field, int being_observed=0.
> The attach() function sets being_observed.  Any code affecting object state
> is obliged to call PyObject_NOTIFY, a macro that checks being_observed and,
> if set, calls notifyall(subject).

doesn't "Any code affecting object state" include an awful lot of places?

   holger