How can I dynamically create objects in django/python?

Question

In my code I have many if/elif statements like this:

if type == "cat":
    vote = VoteCat (
        user = user,
        cat_id = thing_id )
    vote.save()
elif type == "dog":
    vote = VoteDog (
        user = user,
        dog_id = thing_id )
    vote.save()

What would be a good way to change my code to get rid of the if statements and instantiate the object I need dynamically? The code I am hoping I can write would accomplish the same as above but look more like this:

AnimalVote = get_animalvote_by_type(type)
AnimalVote.user = user
AnimalVote.assign_animal_id(thing_id)
AnimalVote.save()

if i'm understanding your question correctly, perhaps the easiest thing to do would be to have an AnimalVote model with a field specifying what type of animal it is. — Kapura
– Kapura, Commented Jan 9, 2013 at 0:11
Since you're using django how about a custom objects manager? — Hedde van der Heide
– Hedde van der Heide, Commented Jan 9, 2013 at 0:12
I've thought doing it your way Kapura but thought that it may not scale as well as I add many different kinds of Animals that have slightly different behaviors. — tedtoy
– tedtoy, Commented Jan 9, 2013 at 0:28

jscs · Accepted Answer · 2013-01-22 20:23:26Z

7

The simplest translation is:

types = dict('cat' = CatType, 'dog' = DogType)
newobj = types[type](user = user, cat_id = thing_id)

Obviously, this relies on the types taking the same parameters.

edited Jan 22, 2013 at 20:23

jscs

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answered Jan 9, 2013 at 0:19

Marcin

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2 Comments

tedtoy Over a year ago

Thank you for the simple, quick answer. I feel like I should have known I could do it this way.

Marcin Over a year ago

@tedtoy It's not entirely obvious until you know about it.

David Z · Accepted Answer · 2013-01-09 00:18:44Z

3

Classes in Python are objects, so you can just have a map mapping names to classes:

animal_type_map = {'cat': VoteCat, 'dog': VoteDog}

Then you can use animal_type_map[type] just as you would use VoteCat or VoteDog.

answered Jan 9, 2013 at 0:18

David Z

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