Python: long if expression vrs. small if blocks

Question

I have this very little and simple if blocks:

if obj_type == "domain":
    key = "domain"
elif obj_type == "db_user":
    key = "username"
else:
    key = "name"

These can be converted to an if expression:
key = "domain" if obj_type == "domain" else "usernme" if obj_type == "db_user" else "name"

Are there any advantages in performance? If that's not a factor, which one should by preferred for readability, PEP8 compliance?

Answer 1

They perform identically, so use the first one if you need to choose between the two.

Since you're really just creating a mapping between two sets, using a dictionary would be a better approach. It's faster and arguably more readable:

mapping = {
    'domain': 'domain',
    'db_user': 'username',
}

key = mapping.get(obj_type, 'name')