Executing a function for each element and correct typing of it

[Sanchoyzer]

Let's look at this code:

import dataclasses

@dataclasses.dataclass
class MyClass:
    x: int
    y: int

    def __init__(self, **kwargs) -> None:
        any(object.__setattr__(self, k, v) for k, v in kwargs.items() if k in self.fields())

    @classmethod
    def fields(cls) -> set[str]:
        return {field.name for field in dataclasses.fields(cls)}


MyClass(**{'x': 1, 'y': 2, 'z': 3})

There is a mypy error:

error: "__setattr__" of "object" does not return a value

Of course, I can write it like a loop, but it'll take three lines instead of one.
What is the correct way (in one line) to execute a function (without returning a result value) for each element from a collection?

[sobolevn]

but it'll take three lines instead of one

Lines are basically free ;)
Plus, this would be ideomatic usage.

The reported error is correct. You cannot use object.__setattr__ with any, it does not make any sense.

[JelleZijlstra]

for k, v in [k, v for k, v in kwargs.items() if k in self.fields()]: object.__setattr__(self, k, v)

[sobolevn]

🙈

[Sanchoyzer]

I can do it shorter, but still not elegant :)

for k in set(kwargs.keys()) & self.fields(): object.__setattr__(self, k, kwargs[k])

[AlexWaygood]

Dictionary keys are a set-like object, so the call to set(kwargs.keys()) is redundant; you can golf it down further to:

for k in kwargs.keys() & self.fields(): object.__setattr__(self, k, kwargs[k])

[jeremyn]

You can also one-line it in __init__ if you create a new function set_attributes(...) and move the logic there. Or, have the caller filter kwargs before passing it to __init__. Also, translating between keys and attributes is something types.SimpleNamespace already does, maybe that could fit in somewhere.