class Hello(object):
	
	def __call__(self, arg):
		return "Hello, %s" % arg
		
		# return "Hello, " + str(arg)
		# return "Hello, {}".format(arg)

		# return f"Hello, {arg}" # Only Python 3.6

	def __str__(self):
		return "Hello, world!"


def main():
	a = Hello()
	print(a('students'))
	print(a)

if __name__ == '__main__':
	main()