class Tester :
	def __str__ (self) :
		return 'Hello world.'

	def __len__ (self) :
		return 13

print (Tester ())
print (len (Tester ()))

Quote:A class can implement certain operations that are invoked by special syntax (such as arithmetic operations or subscripting and slicing) by defining methods with special names. This is Python’s approach to operator overloading, allowing classes to define their own behavior with respect to language operators.

class Spam:
    pass

class Eggs:
    def __str__(self):
        return 'instance of my class Eggs'

spam = Spam() # instance of class Spam
eggs = Eggs() # instance of class Eggs

print(spam)
print(eggs)

Output:
<__main__.Spam object at 0x7fd8d323c978>
instance of my class Eggs