when does the instance methods in a class run in python code example

Example: instance method in python

# Instance Method Example in Python 
class Student:
    
    def __init__(self, a, b):
        self.a = a
        self.b = b 
    
    def avg(self):
        return (self.a + self.b) / 2

s1 = Student(10, 20)
print( s1.avg() )