weakrefs to functions for observer pattern

[Michael Schneider]

Hello All,

I am comming back to python after being away for several years.

I would like to use weak refs in an observer pattern implementation.

The problme that I have seems to be that weakrefs can't manage functions.

------------------- from docs:
http://www.python.org/doc/current/lib/module-weakref.html

Not all objects can be weakly referenced; those objects which can
include class instances, functions written in Python (but not in C),
methods (both bound and unbound), sets, frozensets, file objects,
generators, type objects, DBcursor objects from the bsddb module,
sockets, arrays, deques, and regular expression pattern objects. Changed
in version 2.4: Added support for files, sockets, arrays, and patterns.

-------------------------------------------------------

Is there a technique that I can use to leverage weak references to I
don't have to unregister my observers?

Thanks
Mike

PS. here is the code that I have been working with (Note: I commendout
out the weak ref creation.

--------------------------------------------------------------------
import types
class Observable(object):

def addObserver(self, observer, events=None):
if not hasattr(self, '_observers'):
#self._observers = weakref.WeakKeyDictionary()
self._observers = {}

if observer is None:
return

if events is not None and type(events) not in (types.TupleType,
types.ListType):
events = (events,)
self._observers[observer] = events

def removeObserver(self, callable):
if not hasattr(self, '_observers'):
return

if self._observers.has_key(callable):
del self._observers[callable]

##
# Notify all currently-registered Observers.
#
# This observer will be called if the event is one that the
# Observer is interested in, or if event is 'None'
#
# @param event The event to notify the Observers about. None
# means no specific event.
#
# *args - standard arguments - passed through to observer
# **kw - keyword arguments - passed through to observer
def notifyObservers(self, event=None, *args, **kw):

if not hasattr(self, '_observers'):
return

for cb, events in self._observers.items():
if events is None or event is None or event in events:
if cb is not None:
cb(self, event, *args, **kw)

 

[Alex Martelli]

I would like to use weak refs in an observer pattern implementation.
The problme that I have seems to be that weakrefs can't manage functions.

They can manage just fine functions written in *Python*, just not
"builtin functions*, i.e., ones written in *C*. Just wrap any builtin
function you need to register as observer into a tiny Python-coded
wrapper and live happily ever after.
...

Not all objects can be weakly referenced; those objects which can
include class instances, functions written in Python (but not in C),

Alex

 

[Michael Schneider]

They can manage just fine functions written in *Python*, just not
"builtin functions*, i.e., ones written in *C*. Just wrap any builtin
function you need to register as observer into a tiny Python-coded
wrapper and live happily ever after.
...




Alex

Alex,

Thank you, I mis-read the docs.

The mistake I made was having was using a weak reference as a key in
the dictionary.

Weak references will be very useful for me.

I really enjoy python. So many good things have been added to the
language without taking the fun away

Mike

 

[Alex Martelli]

Thank you, I mis-read the docs.

The mistake I made was having was using a weak reference as a key in
the dictionary.

Rather than using a weakref.WeakKeyDictionary , I guess?

Weak references will be very useful for me.

I really enjoy python. So many good things have been added to the
language without taking the fun away

Glad to hear this!


Alex