The Singleton meta class unexpectedly raises a TypeError when we thought __instance__ existed

[zancas]

In [4]: _RcliConfig.call()

TypeError Traceback (most recent call last)
in ()
----> 1 _RcliConfig.call()

~/rcli/venv/lib/python3.6/site-packages/typet/meta.py in call(cls, args, **kwargs)
78 else:
79 try:
---> 80 cls.instance.singleton(args, **kwargs) # type: ignore
81 except AttributeError:
82 pass

TypeError: 'NoneType' object is not callable

The code in question is here:

https://github.com/contains-io/typet/blob/master/typet/meta.py#L64

[dangle]

Is this fixed with the catch for TypeError?

[zancas]

I still don't understand where the TypeError in question is being raised.

[dangle]

The issue is that __instance__ defaults to None. The if-statement checks for falsey then tries to run it, but then it tries to call __singleton__ on __instance__ which is None. Maybe a better idea would be to change that else to elif cls.__instance__ is not None: instead of catching TypeError.

[dangle]

I think this is fine with the TypeError check. Closing this for now.