🔒 Syntax question/dunders

[hazy marlin]

Can someone help me with this question? I dont understand orders for init

[fleet anchor]

@hazy marlin

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[leaden pebble]

You know the easiest way to figure this out is to add a print statement before each line, and see the output

[plain cobalt]

Do you know about inheritance

[leaden pebble]

Where it says: #line3, change this to print("Line 3")

[hazy marlin]

in case its hard to read

[hazy marlin]

a lil bit

[hazy marlin]

thats like using test cases right?

[leaden pebble]

No, I'm just saying: Run the code.

And add print statements.

[plain cobalt]

I’m assuming if this is homework they will have to know how to do it without running code

[leaden pebble]

This is a very important skill.

[leaden pebble]

Agree... just better to teach a person to fish and all that.

[plain cobalt]

But running code is great for learning

Yeah I agree

But after they add print statements I think we should explain why it’s that order

I’ve gtg tho actually

[surreal shore]

You get the answer?

[hazy marlin]

i tried that and when i ran the code, i got Line 3 in the shell

[surreal shore]

Did you do the other lines too?

[leaden pebble]

Show the code you ran

(my goal was to get them to see the answer via prints, then explain it)

[hazy marlin]

no 😭 my fault one sec

[daring wing]

Orders for __init__ are no different to other functions/methods. You make a Child. That calls its init. The child init calls the parent init, and the parent init calls the grandparent. In exactly the order of the statements in each init method - there's no magic or anything. The only automatic part is the call to Child.__init__. The other calls are explicit in the code.

[leaden pebble]

This is somewhat a trick question because where the line comments are placed.

[hazy marlin]

ahh i got line 2, line 1, line 3

[leaden pebble]

Yah... so let's discuss

[hazy marlin]

i still don't fully understand why it runs in that order though

[leaden pebble]

It's a trick/tricky question because the line 2 is before the super, but line 3 is after the super

So what happens is: Child.__init__ is called first. Does that make sense, for starters?

[hazy marlin]

so the def __init is called before the super init and line 3 is called after the super from line 2?

[leaden pebble]

def __init__ declares the function __init__, it's not really "run", per se, when you call Child(). The function __init__ is called.

[hazy marlin]

what about for GrandParent?

since theres no super()__init__

[leaden pebble]

What's happening is: Child.__init__ is called when you construct Child(). The first step of Child.__init__ calls Parent.__init__. The first step of Parent.__init__ is "Line 2", so that prints first. Then, it calls GrandParent.__init__, whose first line is Line 1.

[hazy marlin]

but why do we not begin at class GrandParent if its line 1?

[daring wing]

It's possible that Neptune is thinking that all the parent and grandparent inits are somehow always called because of the class inheritance. They are not.

Python make an "empty" Child instance and calls its __init__ method to initialise it. That is all. The Child init happens to call the parent init, and the parent init happens to call the grandparent init. But only because those calls are in the code of their init methods.

[leaden pebble]

You need to take a step back and understand what "inheritance" means.

And what a "class" is.

I'm sure your class has some notes, but here's a brief explanation: https://python.swaroopch.com/oop.html

[surreal shore]

I captured a little gif of the debugger in this code. it might help

[hazy marlin]

i understand it now

[leaden pebble]

I'd be very surprised. It took most of us a long time to really understand this stuff. I wasn't trying to be negative: I just meant that you need to take a step back and really get it.

(because we all struggled with it at first)

[hazy marlin]

we use super().__init__ to call for the initializer of the parent and grandparent classes, and Line 2 is executed first because the Child class's __init__ calls the parent classes __init__ method , correct?

[daring wing]

The actions go:

• python calls child init
• child init calls parent init (via super())
• parent init does line 2
• parent init calls grandparent init (via super())
• grandparent init does line 1
• return
• return
• child init does line 3
• return

[hazy marlin]

Line 1 is executed second because the parent classes __init__ method calls the Grandparent class's __init__ method using the super() function and line 3 is executed last because the Child class's __init__ method continues to priont Line 3

[hazy marlin]

yup yup

i got it

[leaden pebble]

And why doesn't grandparent have a super().init?

[daring wing]

Importantly: there's nothing automatic about calling the superclass inits - that's an explicit part of your implementation of the child init.

[hazy marlin]

bc theres no need to call a method from a parent class using super(), theres no further parent class for the grandparent domain

[daring wing]

Aye. technically the parent of GrandParent is object, but its init does nothing 🙂

[hazy marlin]

so unless they come up with a great-grandparent ancestor in the hierarchy thers no method to invoke from the grandparent class

thanks guys

[fleet anchor]

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🔒 Syntax question/dunders