SLOG #1: Object-Oriented Programming

This week we learned about stack superclass, IntStack subclass and raising and catching exceptions. I have never learnt it before.

I feel it was quite useful to learn how to derive subclass from superclass. Since different objects may have something in common. If we could inherit methods from other classes, we could save a lot of work. This also makes the subclass easy to read. At first, I didn't understand why we don't just copy and paste the existing code and modify it. Now I feel if we could inherit from existing code, we could not only save space and time, but also avoid making mistakes in modification.

It is also quite helpful to learn how to write programs to handle exceptions. I felt frustrated for not fully understanding how raising and catching exceptions works at first. Exceptions are also classes. This identification helps me understand how exceptions work in the code. Like some other classes, exceptions should be typically derived from other Exception classes. We could use the raise statement to create a specified exception to test our code. The really confusing part is the first triggered matching except clause will be executed in raise statement.

A similar example from python official website:

class B(Exception):

    pass

class C(B):

    pass

class D(C):

    pass

for cls in [B, C, D]:

    try:

        raise cls()

    except B:

        print("B")

    except C:

        print("C")

    except D:

        print("D")

It would have printed B, B, B, instead of B, C, D.

Please feel free to leave comments here. I would be happy to discuss programming with you.