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

[Josef Pktd]

On Monday, November 30, 2015 at 8:01:14 PM UTC-5, Steven D'Aprano wrote:
> 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?

I'm using dir and vars pretty often when I'm trying to figure out new code or review a pull request, or when I'm reviewing code that I don't remember.

Both are convenient for quickly checking which attributes are available at the moment. I never realized that there might be issues with "fancy" problems. 

`vars` is convenient, for example, to check which attributes have been initialized to None, and which already have assigned values. And checking again after some calculations, I roughly see which attributes have been added or changed in the mean time.

aside: I'm boring and like code that has no magic, especially if I have to maintain it.

Josef

> 
> 
> 
> -- 
> Steven