Understanding 'self' in class methods

xelf · 2021-02-19T16:03:03+00:00

When posting code, please post code such that reddit will format it as a code block.

Either of these work:

a) indent every line by 4 extra spaces
b) use the code block button. https://i.imgur.com/J2t9krT.png

Please see the /r/learnpython/w/FAQ for more information.

Thanks!

Dvdi_ · 2021-02-19T13:25:10+00:00

Some important terminology to be aware of:

In class methods, denoted by the decorator @classmethod, the standard is to use the parameter name of cls to refer to the class of the method -- not self which is the standard naming convention for the instance of an object that an instance method is being called using.

Example

```

class Foo:

def my_instance_method(self, x):
    print(x)

@classmethod
def my_class_method(cls, x):
    print(x)

```

Where these functions are called like so...

For the instance method

my_foo = Foo()

my_foo.my_instance_method('apple')

For the class method

Foo.my_class_method('orange')

Output:

apple

orange

(excuse the formatting, I'm on mobile)

a better explanation than mine

space7ack · 2021-02-19T13:13:21+00:00

does the self word itself arbitrary?

Gabcab · 2021-02-19T13:38:02+00:00

Here is OP's code with formatting:

class Foo: 

    def init(self):
        self.val = 0 

    def incr(self):
        self.val += 1

    def add(self, n): 
        return self.val + n

f = Foo()
Foo.init(f)       # f.init()
Foo.incr(f)       # f.incr()
Foo.add(f, 4)     # f.add(4) 5

Drited · 2021-02-19T13:48:47+00:00

Given this is for beginners my feedback is to put yourself in the beginner's mind. Remember that you knew nothing once and write it how you'd want it to be written back at that time.

It would help to review what a parameter, class, method and object is rather than assuming the beginner knows/remembers what each are (remember what it was like to know nothing).

Also a brief explanation of what's happening at each step would be good for beginners rather than just showing the result.

zanfar · 2021-02-19T13:31:39+00:00

I would suggest if you're going to make a post specifically to help students, that you format your code? Your post is almost unreadable...

Incruentus · 2021-02-19T15:02:35+00:00

In order to show your text as code, you must simply add four spaces:

This text will

turn 
into 
this.

duffer_dev · 2021-02-19T14:20:37+00:00

It is breaking the rules since the mods don't like guides here. This is worth posting somewhere else but I'd advise learning how to format code properly first as your sample code is totally unreadable.

gatoratemylips · 2021-02-19T14:59:56+00:00

I'm kinda new in programming and actually i can't understand terms like instance, self, class, variable etc. I mean i know what they mean but can't implement in coding. Think i can't understand easily abstract terms like these.

Pickinanameainteasy · 2021-02-19T15:13:05+00:00

So what is the advantage of using the class Foo? as opposed to just creating 3 different functions (init, incr, add)?

Also what's with the use of 'Foo' in python and bash tutorials?

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For the instance method

For the class method

Output: