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"""
from Thinking in Python, Bruce Eckel
http://mindview.net/Books/TIPython
Class support for "observer" pattern.
The observer class is the base class
for all smartcard package observers.
Known subclasses:
smartcard.ReaderObserver
"""
from smartcard.Synchronization import *
class Observer:
def update(observable, arg):
'''Called when the observed object is
modified. You call an Observable object's
notifyObservers method to notify all the
object's observers of the change.'''
pass
class Observable(Synchronization):
def __init__(self):
self.obs = []
self.changed = 0
Synchronization.__init__(self)
def addObserver(self, observer):
if observer not in self.obs:
self.obs.append(observer)
def deleteObserver(self, observer):
self.obs.remove(observer)
def notifyObservers(self, arg=None):
'''If 'changed' indicates that this object
has changed, notify all its observers, then
call clearChanged(). Each observer has its
update() called with two arguments: this
observable object and the generic 'arg'.'''
self.mutex.acquire()
try:
if not self.changed:
return
# Make a local copy in case of synchronous
# additions of observers:
localArray = self.obs[:]
self.clearChanged()
finally:
self.mutex.release()
# Update observers
for observer in localArray:
observer.update(self, arg)
def deleteObservers(self):
self.obs = []
def setChanged(self):
self.changed = 1
def clearChanged(self):
self.changed = 0
def hasChanged(self):
return self.changed
def countObservers(self):
return len(self.obs)
synchronize(Observable,
"addObserver deleteObserver deleteObservers " +
"setChanged clearChanged hasChanged " +
"countObservers")
#:~
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