python call methods from super class

Question

I am trying to understand python inheritance a little. Here is a use case:

class Test:

    def hello():
        print("hello")
        return "hello"

    def hi():
        print(hello())
        print("HI")

class Test1(Test):
    hi()
    pass

x = Test1()
x.hello()

I don't understand why I can't call "hi()" in class Test1. It inherited it class Test right?

Because that's not how you call methods inside classes. What are you attempting to do by writing that call at the class level? — Daniel Roseman, Sep 12 '17 at 08:40
Well, I figure since Test1 inherits Test, it should be able to call it at class level right? — ozn, Sep 12 '17 at 08:42
I think what you wanted to do is to call `hi()` from the object `x`. (e.g. after `x.hello()` call `x.hi()` and it will work as expected) — Jerrybibo, Sep 12 '17 at 08:42
I want to call "hi()" from Test1 class, not necessarily create an object. — ozn, Sep 12 '17 at 08:43
Then you are not using classes in any understandable way. Classes are *for* creating objects. You need to explain *why* you would want to do something different. — Daniel Roseman, Sep 12 '17 at 08:44
@DanielRoseman: Well thats what I am trying to understand. is this valid? — ozn, Sep 12 '17 at 08:44

Jerrybibo · Answer 1 · 2017-09-12T09:05:11.147

I think you are misunderstanding the relationship and definitions of classes and objects. Classes are like blueprints to create objects. By writing methods inside a class, you are essentially defining the behaviors of the object that can be created from the class blueprint. So, with your code:

class Test:

    def hello():
        print("Hello")
        return "Hello"

    def hi():
        print(hello())
        print("Hi")


class Test1(Test):

    hi() # <- You really shouldn't call a method directly from a "blueprint" class
    pass

x = Test1()
x.hello()

While your last two lines of code are valid, it's a bad idea (and almost always invalid) to call a method outside of the class's scope directly inside a class definition. The reason why hi() does not work in the Test1 class is that it's not defined in the scope of Test1; even though this class indeed inherits from the Test class, it only affects the object that is created from the class (like the object x you created from the Test1() class).

Here's a more detailed explanation about classes and objects from another relevant question: What are classes, references and objects?

Hope this helped!

python call methods from super class

1 Answers1