python - Use `__dict__` or `vars()`?

56
votes

Builtin function vars() looks more Pythonic to me, but I see __dict__ used more frequently.

The Python documentation indicates that they are equivalent.

One blogger claims that __dict__ is faster than vars().

Which shall I use?

3
python
It depends what you're trying to do. In many cases, neither approach is the Right Way. In this broad a question, it seems that both work fine. - Adam Smith
I generally go with __dict__ just to avoid another layer of parentheses. Flat is better than nested and all. - user2357112 supports Monica
I guess __dict__ being slightly faster is no surprise. Accessing object attributes is faster than calling a function. - aIKid
I don't know why but using vars seems cooler, and a little more neat. I can imagine this is more useful for beginners. It would be easier to explain, "Getting the vars of an object". - aIKid
To me __dict__ is more intuitive because I get back dict representation of an object. - Akavall

3 Answers

25
votes

I'd use vars().

From: https://wiki.python.org/moin/DubiousPython#Premature_Optimization

While a correctly applied optimization can indeed speed up code, optimizing code that is only seldom use [..] can make code harder to read. [..] Write correct code first, then make it fast (if necessary).

From: The Zen of Python

Readability counts.

67
votes

Generally, you should consider dunder/magic methods to be the implementation and invoking functions/methods as the API, so it would be preferable to use vars() over __dict__, in the same way that you would do len(a_list) and not a_list.__len__(), or a_dict["key"] rather than a_dict.__getitem__('key')

15
votes

I agree vars should be preferred. My rationale is that, as python evolves, vars might be extended to do more than __dict__ does (for example, work for objects with slots, possibly in 3.7).