What is the purpose of varB = self(varA) in a Python class?

Question

I am debugging a Python code and see this code pattern in one of the classes:


def someOtherFunction (x):
    return x**2

class baseX():
    pass

class baseY():
    pass


class newBase (baseX, baseY):

    def __init__ (self, **kwargs):
        super().__init__(**kwargs)
    
    def func (self, varX):
        varA = someOtherFunction(varA)
        varB = self(varA)
        return varB

I am having a hard time understanding the self() syntax. What is varB = self(varA)? What is it doing?

The original code is not my code. The original code is supposed to work. The pseudo-code I wrote is to represent my question better. Please see the original code on Github (Line 101)

DoingSomething ==> `NameError` ... stop pseudocoding and add a [mre]. — Patrick Artner, Nov 12 '21 at 06:48
Also `self(varA)` will definitely raise an error as (1) `varA` is not defined and (2) the class instance is not a callable. — Selcuk, Nov 12 '21 at 06:49
[https://stackoverflow.com/questions/9663562/what-is-the-difference-between-init-and-call](https://stackoverflow.com/questions/9663562/what-is-the-difference-between-init-and-call) — Patrick Artner, Nov 12 '21 at 07:03
@Selcuk-the code is not mine, I am just reading/goingThrough it. I just wrote a psudo code of it. The code is suppose to work. and about your comment "the class instance is not a callable". This is my question! Why they clled it? — Sajjad Kavyani, Nov 12 '21 at 14:48
@Patrick Artner. Thank you for the link. that solved my problem — Sajjad Kavyani, Nov 12 '21 at 15:51

score 1 · Accepted Answer · answered Nov 12 '21 at 06:52

First, you need provide a MRE. Such as when you defined a class, dont use def before class
I try to fix the bug in your code to a MRE

def someOtherFunction(x):
    return x+1

class baseX:
    pass

class baseY:
    pass

class newBase (baseX, baseY):

    def __init__ (self, someARGS):
        self.varA = someARGS

    def __call__(self,x):
        return x + 5

    def func (self, varX, varA):
        varX = someOtherFunction(varX)
        varB = self(varA)
        return varB

x = newBase(5)
print(x.func(0,10))

#result : 15

In this code, the self(varA) represent to call newBase as a callable object, which normal class is not callable.

Thank you SO much. I think you just nailed it! That __call__() method was my problem. It seems in one of the upper classes (please see the Github for the actual code) there is a __call__() method that is passed to the child class "newBase". And so it is now can be called. Thanks again. — Sajjad Kavyani, Nov 12 '21 at 15:39

What is the purpose of varB = self(varA) in a Python class?

1 Answers1