Puzzle with staticmethod in a class variable I can't figure out

Question

I'm trying to make a class static method, and then use it in a class variable as a callback. I'm running into a problem with the static method not being callable that I can't figure out:

from dataclasses import dataclass from typing import Callable @dataclass class Option: txt: str callback: Callable class Window: @staticmethod def _doit(a=1): print('do it with a', a) cvar = Option(txt='doit', callback=_doit) w1 = Window() w1._doit() # works fine Window._doit() # works fine w1.cvar.callback() # this fails

The last call above fails with "TypeError: 'staticmethod' object is not callable".

I'm not sure why here, but even more confusing to me is if I remove the @staticmethod line, then things work 'correctly' - with all 3 calls in the code working.

I know I must being doing something stupid wrong, but I can't figure out what's wrong with the above ...any help?

thanks!

rhurwitz · Accepted Answer · 2021-02-18 22:41:44Z

EDIT: Oops, @Richard correctly pointed out that my original example was broken - I did not see the error since I had already defined the Window class running the original code. A bit tricky, but here is a version that should work along with a more detailed explanation.

EDIT #2: Sigh, fixed another typo. :^(

Example:

cvar = Option(txt='doit', callback=_doit.__func__)

Thanks - that was my first thought, which I tried. ...but that fails, with name 'Window' is not defined.
...thanks! ...note you need to edit your answer to remove the () after func ...otherwise it will execute the function, not point to the function.

Richard · Accepted Answer · 2021-02-18 20:32:27Z

Thanks to the comment above, I checked this previous answer to similar question.

To correct the code above - where you're trying to reference a static method before it's bound - you need to reference the function location directly:

class Window: @staticmethod def _doit(a=1): print('do it with a', a) cvar = Option(txt='doit', callback=_doit.__func__)

The other option (which I'd already found worked, but preferred to identify my function explicitly as a staticmethod, was to remove the staticmethod decorator.

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