Checking for member existence in Python

Question

I regularly want to check if an object has a member or not. An example is the creation of a singleton in a function. For that purpose, you can use hasattr like

Answer 1

It depends on which case is "typical", because exceptions should model, well, atypical conditions. So, if the typical case is that the instance attribute should exist, then use the second code style. If not having instance is as typical as having instance, then use the first style.

In the specific case of creating a singleton, I'm inclined to go with the first style, because creating a singleton the initial time is a typical use case. :-)