def __str__

__str__ is a special method in Python that is used to return a string representation of an object. It is invoked when an object is passed to the built-in str() function or when the object is used in a string context (such as when it is printed).

For example, suppose we have a class called Person with instance variables name and age:

class Person:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def __str__(self):
        return f"{self.name} is {self.age} years old"

The __str__ method is defined to return a string that describes the object. In this case, it returns a string that concatenates the person's name and age.

When we create a Person object and print it:

p = Person("Alice", 30)
print(p)

The __str__ method is invoked automatically, and the output will be:

Alice is 30 years old