How to pass reference of a class parameter value to a function default argument value within the same class

Question

I want to pass the value supplied to the class parameter to a function in the same class as it's default arguments, so that i could reuse the function to do another calculation with a different parameter value.

I'm working on creating an ip address calculator as a challenge for me to help learn python programming.

But Pycharm says "Unresolved reference 'self' "

Code:

class IPOctet:

    def __init__(self, ip_address, subnet_mask):
        self.ip_address = ip_address
        self.subnet_mask = subnet_mask

    def validate_subnetmask(self, input_subnetmask = self.subnet_mask):
        # this function validates the input_subnetmask value to check if its a numeric value and 
        # returns the value when validated.

        # ...and i want the [input_subnetmask value] to be [self.subnet_mask] as its default arugument
        #  or any value passed into it when called.

Function default values are evaluated at the time the function was originally defined. The *class* didn't even exist yet, much less any instance of the class to have a meaningful `self` value. — jasonharper, Aug 20 '20 at 16:07
Also: https://stackoverflow.com/questions/7371244/using-self-as-default-value-for-a-method and https://stackoverflow.com/questions/8131942/how-to-pass-a-default-argument-value-of-an-instance-member-to-a-method — Tomerikoo, Aug 20 '20 at 16:12

Banana · Accepted Answer · 2020-08-20T16:07:03.700

2

Use another default value and then check:

def validate_subnetmask(self, input_subnetmask=None):
    if input_subnetmask is None:
        input_subnetmask = self.subnet_mask

even shorter thanks to @CamiEQ:

def validate_subnetmask(self, input_subnetmask=None):
    input_subnetmask = input_subnetmask or self.subnet_mask

edited Aug 20 '20 at 16:07

answered Aug 20 '20 at 16:02

Banana

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you could make it even shorter: `input_subnetmask = input_subnetmask or self.subnet_mask` – CamiEQ Aug 20 '20 at 16:04
ok so do this need an else statement? – Kwame Benqazy Aug 20 '20 at 16:07
@KwameBenqazy No, just write your code under this function definition. – Banana Aug 20 '20 at 16:09
2

@CamiEQ I think much better to be explicit. We don't know what type `input_subnetmask` is, and it is possible for example that a valid mask representing `0.0.0.0` might be falsy. – alani Aug 20 '20 at 16:15

How to pass reference of a class parameter value to a function default argument value within the same class

1 Answers1