What is the name of this python programming concept (passing a class type as an argument)?

Question

What's the best name to describe this:

class Animal(object):
    def __init__(self,animal_type):
        self.animal = animal_type()

class Dog(object):
    def __init__(self):
        pass

fido = Animal(Dog)

?

In particular, this line:

self.animal = animal_type()

Basically what is happening is I'm passing the type of the class I want to initialize as a parameter.

TIA, Noah

Answer 1

Depending on how you use it, it might be the Decorator pattern

EDIT: Just to make it clear, the decorator pattern is not Python specific, it's an object-oriented design pattern applicable to any object-oriented language.

Regarding the line self.animal = animal_type(), what you are actually doing is calling a Python type, which returns a new instance.

For example, you could instance an integer by calling the integer type:

>>> a = int()
>>> a
0
>>> type(a)
<type 'int'>
>>> a = int(3)
>>> a
3
>>>

As you can see, you can also pass parameters to a type when calling it, which will be used for initialization. In your case, you are instancing a Dog object by passing the class type (which is just another Python object). I'm not sure if there's a specific name for this.

Answer 2

It would probably be suitable to say that types are "first class objects" in Python, meaning that they can be passed around just like any other object.

Answer 3

I don't know if there is an "official" name for it, but I think a good name would be type injection.

Answer 4

It's called a class factory: an object that, when called as a function, instantiates and returns an object. All Python classes are also class factories. It's not often referred to as that in Python, since it's such an implicit concept in this language, but if you're looking for a name, that's what you're looking for.