[Python] Type hint warning `"keys" is not a known attribute of "None"` for `Optional` in...

Recently Pylance has started to add red underlines in my code. I've managed to fix most of it, but I have problems with Optional typing:

def realms(testenv:str, active:bool=True) -> Optional[Dict]:
""" return a dict of active/inactive realms with info from keycloak, on error return None """
dat = api(testenv, endpoint="/admin/realms")
:

all_realms = list(realms(testenv, active=False).keys())
------


Pylance says:

"keys" is not a known attribute of "None"
​

If I change the def prototype to:

def realms(testenv:str, active:bool=True) -> Dict:


I get small issues with return None I can fix with raise exceptions, or just remove it.

The code workaround can be a two-liner:

all_realms_dict = realms(testenv, active=False)
all_realms = list(all_realms_dict.keys()) if all_realms_dict else []


Should I stop using Optional and switch to raising exceptions? Is returning None a bad idea?

Continue reading...