"""
Ex. 5.10 from "A primer on..."
From the shown usage of the class we see that it
needs two special methods __call__ and __str__.
"""


class Hello:
    def __init__(self):
        self.greeting = 'Hello, '

    def __call__(self, arg):
        return self.greeting + arg + '!'

    def __str__(self):
        return self.greeting + 'World!'

a = Hello()
print(a('students')) #output: Hello, students!
print(a)            #Hello, World!


"""
Terminal> python Hello.py 
Hello, students!
Hello, World!
"""