class Publisher:  
    def __init__(self):  
        self.observers = []  
 
    def add(self, observer):  
        if observer not in self.observers:  
            self.observers.append(observer)  
        else:  
            print(f'Failed to add: {observer}')  
 
    def remove(self, observer):  
        try:  
            self.observers.remove(observer)  
        except ValueError:  
            print(f'Failed to remove: {observer}')  
 
    def notify(self):  
        [o.notify(self) for o in self.observers]  
 
class DefaultFormatter(Publisher):  
    def __init__(self, name):  
        Publisher.__init__(self)  
        self.name = name  
        self._data = 0  
 
    def __str__(self):
        return f"{type(self).__name__}: '{self.name}' has data = {self._data}"
 
    @property  
    def data(self):  
        return self._data  
 
    @data.setter  
    def data(self, new_value):  
        try:  
            self._data = int(new_value)  
        except ValueError as e:  
            print(f'Error: {e}')  
        else: 
            self.notify()  
 
class HexFormatterObs:  
    def notify(self, publisher):  
        value = hex(publisher.data)
        print(f"{type(self).__name__}: '{publisher.name}' has now hex data = {value}")  
 
class BinaryFormatterObs:  
    def notify(self, publisher):  
        value = bin(publisher.data)
        print(f"{type(self).__name__}: '{publisher.name}' has now bin data = {value}")  
 
def main():  
    df = DefaultFormatter('test1')  
    print(df)  
 
    print()  
    hf = HexFormatterObs()  
    df.add(hf)  
    df.data = 3  
    print(df)  
 
    print()  
    bf = BinaryFormatterObs()  
    df.add(bf)  
    df.data = 21  
    print(df)  
 
    print()  
    df.remove(hf)  
    df.data = 40  
    print(df)  
 
    print()  
    df.remove(hf)  
    df.add(bf)  
 
    df.data = 'hello'  
    print(df)  
 
    print()  
    df.data = 15.8  
    print(df)  
 
if __name__ == '__main__':  
    main()