Question

code goes first:

def singleton(cls):
    instances = {}
    def get_instance():
        if cls not in instances:
            instances[cls] = cls()
        return instances[cls]
    return get_instance

@singleton
class A:
    #...

Ok, the code above is an implementation of Singleton, I saw this implementation in another post.

I don’t understand why the singleton function returns a function but A is a class.
How does it worK?

Answer 1

A isn’t a class in the end. The class A gets created, but then replaced with the function that singleton returns. So in the end, A ends up being a function.

But since you call a class to create a object, it ends up working pretty much the same way. But isinstance won’t work.

P.S. you probably shouldn’t use a singleton. In python it is almost always the wrong choice.