Dynamically call staticmethod in Python

Question

I have a python object that has various attrs, one of them is check=None.

class MenuItem:
    check: bool = True

During the __init__() process, it parses it's own attrs and looks if they are callable. If so, it calls the function, and replaces it's instance variable with the result of the function:

    def __init__(self):
        self.request = ...
        if callable(self.check):
            self.check = self.check(self.request)

The purpose is to have subclasses that may replace class attrs by lambda functions:

class MainMenuItem(MenuItem):
    check = lambda request: request.user.is_authenticated

So far, so good. But as the calling of instance methods implicitly adds self as first parameter, I would have to write every lambda (or external function) as lambda self, request: ... - external functions must be def check_superuser(self, request): ... - which IMHO looks bad.

Is there a way in Python to call a function from a method "as staticmethod"? Like

if callable(self.check):
    self.check = staticmethod(self.check)(self.request)

(this obviously doesn't work)

Any hint's welcome. Do I completely think wrong?

Are you maybe looking for an impedance matcher, which discards 1st arg (self) when dispatching to the "real" lambda function? Also, consider using named functions instead of lambdas. For one thing, you can @decorate them. — J_H
– J_H, Commented Nov 21, 2022 at 20:43
in which part of MenuItem the check variable becomes callable? — cards
– cards, Commented Nov 21, 2022 at 21:52
@JuanIsFree, no, I can't declare the attribute as staticmethod in the first place. @cards: in my real code too, it "becomes" callable at declaration time of inherited classes. It's indeed a MenuItem, and eg AdminMenu declares check=lambda request: request.user.is_superuser. @J_H: this is way to complicated for this approach. Meanwhile @Antony Hatchkins has answered it already - this is what I sought. Thanks all. — nerdoc
– nerdoc, Commented Nov 22, 2022 at 20:34

Antony Hatchkins · Accepted Answer · 2022-11-21 20:39:23Z

2

Is this what you are looking for?

class A:
    check: bool = True
    def __init__(self):
        self.request = 'request'
        if callable(self.check):
            self.check = self.__class__.check(self.request)

class B(A):
    check = lambda request: len(request)

b = B()
print(b.check)

outputs 7

answered Nov 21, 2022 at 20:39

Antony Hatchkins

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1 Comment

nerdoc Over a year ago

Thanks. I always tried to fix it with type(self).check(self.request). But obviously this is calling the Metaclass' check method - which is kind of the same, but it did not work properly. Thanks a bunch.

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