In Python, what's the correct way to instantiate a class from a variable?

Question

Suppose that I have class C.

I can write o = C() to create an instance of C and assign it to o.

However, what if I want to assign the class itself into a variable and then instantiate it?

For example, suppose that I have two classes, such as C1 and C2, and I want to do something like:

if (something):
   classToUse = C1
else:
   classToUse = C2

o = classToUse.instantiate()

What's the syntax for the actual instantiate()? Is a call to __new__() enough?

Answer 1

o = C2()

This will accomplish what you want. Or, in case you meant to use classToUse, simply use:

o = classToUse()

Hope this helps.

Answer 2

You're almost there. Instead of calling an instantiate() method, just call the variable directly. It's assigned to the class, and classes are callable:

if (something):
    classToUse = C1
else:
    classToUse = C2

o = classToUse()

Answer 3

It's simple, Python don't recognize where a varible is a class or function. It's just call that value.

class A:
   pass
B=A
b=B()

Answer 4

A class is an object just like anything else, like an instance, a function, a string... a class is an instance too. So you can store it in a variable (or anywhere else that you can store stuff), and call it with () no matter where it comes from.

def f(): print "foo"

class C: pass

x = f
x() # prints foo

x = C
instance = x() # instanciates C