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

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

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


a = Hello()
print(a('students'))
print(a)

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