observer_exercise.py

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from .observer_class import ObserverForDecimal, ObserverForHexaDecimal, ObserverForBinary
from .observersubject_numberproducer import ObserverSubject_NumberProducer
 
 
 
# ! [Using Observer in Python]
def Observer_Exercise():
    print()
    print("Observer Exercise")
 
    numberProducer = ObserverSubject_NumberProducer()
 
    # The number producer is passed to the observers so the observers
    # can get the number to display.  The observers only see the
    # INumberProducer interface, to minimize knowledge about the
    # Subject.
    observerDecimal = ObserverForDecimal(numberProducer)
    observerHexadecimal = ObserverForHexaDecimal(numberProducer)
    observerBinary = ObserverForBinary(numberProducer)
 
    # Tell the number producer about the observers who are notified
    # whenever the value changes.
    numberProducer.SubscribeToNumberChanged(observerDecimal)
    numberProducer.SubscribeToNumberChanged(observerHexadecimal)
    numberProducer.SubscribeToNumberChanged(observerBinary)
 
    # Call the number producer's Update() method a number of times.
    # The observers automatically print out the current value in
    # different bases.
    for index in range(0, 10):
        print("  Update {0} on number producer.  Results from observers:".format(index))
        numberProducer.Update();
 
    # When done, remove the observers from the number producer.
    # It's always good to clean up after ourselves.
    numberProducer.UnsubscribeFromNumberChanged(observerDecimal)
    numberProducer.UnsubscribeFromNumberChanged(observerHexadecimal)
    numberProducer.UnsubscribeFromNumberChanged(observerBinary)
 
    print("  Done.")
# ! [Using Observer in Python]