Starting in Python 3.8, and the introduction of assignment expressions (PEP 572) (:= operator), it’s possible to use a local variable within a list comprehension in order to avoid calling the same function twice.
In our case, we can name the evaluation of map_to_obj(v) as a variable o while using the result of the expression to filter the list; and thus use o as the mapped value:
[o for v in [v1, v2, v3, v4] if (o := map_to_obj(v))]