Python destructing two objects when (I think) I only destructed one

I am learning Python and decided to create a simple class to help me understand. The class is for Tennis Balls.
I have a class attribute of num_balls, and instance attributes of serial_number and age.

I create two instances of the TennisBall class and name them ‘a’ and ‘b’. When I call the destructor for ‘a’, instance ‘b’ also gets destructed.

class TennisBall:
    ball_count = 0    
    
    def __init__(self, serial_number, age):
        self.serial_number = serial_number
        self.age = age
        print("New Tennis Ball created {}!".format(self.serial_number))
        TennisBall.ball_count +=1
        
    def __del__(self):
        print("Tennis ball {} has been deleted :(".format(self.serial_number))
        TennisBall.ball_count -= 1
        
        
        

a = TennisBall(1234, 0)
print("Num balls: {} ".format(TennisBall.ball_count))

b = TennisBall(2345, 0)
print("Num balls: {} ".format(TennisBall.ball_count))

del a
print("Num balls after del ball a: {} ".format(TennisBall.ball_count))

I destructed instance ‘a’ and it was deleted as expected. However, instance ‘b’ was also destructed, even though I did not call that.

I tried destructing ‘b’ instead and again both ‘a’ and ‘b’ were destructed.

>Solution :

This is expected behavior.

When a program terminates, all objects remaining in its memory are deleted (which means that their destructors will be called).

When I run the program, the print statement for Tennis ball 2345 has been deleted :( is executed after the print statement for Num balls after del ball a: 1. In other words, the destructor for ball b is called when the program terminates, after all the code has been executed.