This code snippet was based on the nice recipe 439356 made by Patrick Chasco. My implementation supports only class methods callbacks. I'm keeping the idea of use weakrefs to avoid the interpreter keep the object allocated because the signal is registered (i.e. the signal object holds a reference to callback method). IMO the usage of WeakValueDictionary made the code smaller and clear and also are maintenance-free (when the object is collect by the garbage collector the signal is automatically unregistered).
Python, 68 lines
Download
Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 | """
File: signal.py
Author: Thiago Marcos P. Santos
Created: August 28, 2008
Purpose: A signal/slot implementation
"""
from weakref import WeakValueDictionary
class Signal(object):
def __init__(self):
self.__slots = WeakValueDictionary()
def __call__(self, *args, **kargs):
for key in self.__slots:
func, _ = key
func(self.__slots[key], *args, **kargs)
def connect(self, slot):
key = (slot.im_func, id(slot.im_self))
self.__slots[key] = slot.im_self
def disconnect(self, slot):
key = (slot.im_func, id(slot.im_self))
if key in self.__slots:
self.__slots.pop(key)
def clear(self):
self.__slots.clear()
# Sample usage:
class Model(object):
def __init__(self, value):
self.__value = value
self.changed = Signal()
def set_value(self, value):
self.__value = value
self.changed() # Emit signal
def get_value(self):
return self.__value
class View(object):
def __init__(self, model):
self.model = model
model.changed.connect(self.model_changed)
def model_changed(self):
print "New value:", self.model.get_value()
model = Model(10)
view1 = View(model)
view2 = View(model)
view3 = View(model)
model.set_value(20)
del view1
model.set_value(30)
model.changed.clear()
model.set_value(40)
|
Structures in weakref module such as WeakKeyDictionary and WeakValueDictionary are very powerful for object caching. You can use the object id() as key in your WeakValueDictionary. This id is unique for each instance.
Good.But how to disconnect when calling the signal.
model.changed.disconnect(view1.model_changed)
i.e: You must call the signal's disconnect method using the slot as parameter.