Use default_factory instead of calling the method in dataclass

[hussein-awala]

The method get_airflow_extras is called each time we import the module, which we can avoid by defining the attribute as a filed and setting the method as a default factory.

[Taragolis]

AFAIK it is exact the opposite, default values assigned exactly once, as well as module imports exactly once, if do not count manual reload through importlib or clear sys.modules

The problem with callable on default arguments that if it becomes mutable it will have all side effects of mutable.

In the current proposal this function will call each time when new object of this dataclass instantiated

From what I can tell, it is actually better to just call the function once. If we want to switch to default_factory (which is not unreasonable; import-time logic is bad in general), we need to cache the function.

[hussein-awala]

AFAIK it is exact the opposite, default values assigned exactly once, as well as module imports exactly once, if do not count manual reload through importlib or clear sys.modules

The problem with callable on default arguments that if it becomes mutable it will have all side effects of mutable.

In the current proposal this function will call each time when new object of this dataclass instantiated

I agree with this, but running the method at import time is often (if not always) not recommended, I added a lru_cache as TP suggested. WDYT?

[potiuk]

With cache it's good.