Is vars() the most useless Python built-in ever?

[Steven D'Aprano]

I'm trying to understand why vars() exists. Does anyone use it?

Every time I try to use it, I find it doesn't quite do what I want. And even
if it did, there are more obvious and/or correct alternatives.

For instance, I want to check whether a particular name is an instance
attribute. So first I write:

"name" in obj.__dict__

but when I see the dunder name I think that's an implementation detail. And
sure enough, not all instances have a __dict__ (e.g. if it uses __slots__
instead) and so I re-write it as:

"name" in vars(obj)

but that also fails if obj has no instance __dict__.

But why am I looking just in the instance __dict__? Chances are I should be
looking for the attribute *anywhere* in the instance/class/superclass
hierarchy: 

hasattr(obj, "name")

Or, if you are worried about triggering dynamic attributes using
__getattr__, you can do this:

sentinel = object()
inspect.getattr_static(obj, "name", sentinel) is not sentinel

which only checks for pre-existing attributes without triggering
__getattr__, __getattribute__, or the descriptor protocol.


Either way, vars() doesn't solve the problem. What problem does it solve?



-- 
Steven