Passing class objects to another class method Python

Question

I am trying to understand where my mistake lies and I was hoping you could please help me.

I have this code:

import copy
class FooInd():
    def __init__(self):
        self.a=1

class Planning():
    def foo(self,pop):
        print(pop.a)

    def main():
        ind=FooInd()
        Planning.foo(copy.deepcopy(ind))
if __name__ == "__main__":
    Planning.main()

However I keep receiving this error:

Planning.foo(copy.deepcopy(ind))
TypeError: foo() missing 1 required positional argument: 'pop'

I believe that the mistake is not in the foo method definition, but in my class initiation of the FooInd, however I have checked the Python documentation for classes and I could not find a solution.

Does anyone have a clue of what could I try or where can I check? Many thanks in advance!

Planning.foo takes one parameter in addition to the Planning instance self. — MisterMiyagi
– MisterMiyagi, Commented Dec 2, 2020 at 12:17

ShadowRanger · Accepted Answer · 2020-12-02 12:18:12Z

1

You call Planning.foo on the class, not an instance of the class. You provided the second argument it requires, but not the self argument.

You have two choices:

Construct a Planning instance to call foo on:

def main():
    ind=FooInd()
    Planning().foo(copy.deepcopy(ind))
    #       ^^ Makes simple instance to call on

Make foo a classmethod or staticmethod that doesn't require an instance for self:

class Planning():
    @staticmethod  # Doesn't need self at all
    def foo(pop):
        print(pop.a)

answered Dec 2, 2020 at 12:18

ShadowRanger

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3 Comments

dtkx Over a year ago

Thank you so much! That saved me, I was completely clueless! It makes perfect sense!

ShadowRanger Over a year ago

@dtkx: You're welcome. A heads up: Typically, main is a top-level function, not a method of a class. As written, main isn't even a real method (it doesn't take self, nor is it a @staticmethod, so attempting to call it on an instance of the class would fail); your code only works because it calls it on the class itself. I'd recommend dedenting main out of Planning, and invoking it as plain main() (not Planning.main()) to make it a bit more idiomatic. Sure, a @staticmethod would make it work (whether called on class or instance), but it's silly to make it part of the class.

dtkx Over a year ago

Thank you so much again! Once again it makes total sense, as you could realize I am new to classes, I am still trying to figure out best practices, organization and trade offs between classes and functions. Your advice certainly helped a lot. Thanks again :)

quamrana · Accepted Answer · 2020-12-02 12:16:56Z

1

I think you meant to instantiate Planning before calling methods on it:

import copy
class FooInd():
    def __init__(self):
        self.a = 1

class Planning():
    def foo(self, pop):
        print(pop.a)

    def main(self):
        ind = FooInd()
        self.foo(copy.deepcopy(ind))
if __name__ == "__main__":
    p = Planning()
    p.main()

Output:

answered Dec 2, 2020 at 12:16

quamrana

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1 Comment

dtkx Over a year ago

Thaanks! Thats the direction I was missing!

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