Python - Problem in understanding Monostate design pattern code

I have seen this peice of code in a tutorial regarding Monostate design pattern in Python:

class BookShelf:
    _shared_state = {}

    def __init__(self, number_of_books):
        self.number_of_books = number_of_books

    def __new__(cls, *args, **kwargs):
        object_ = super().__new__(cls)
        object_.__dict__ = cls._shared_state
        return object_

When I tested this code, it works as the class addresses are different while the number_of_books is shared between them. I don't understand how the number_of_books is passed to the _shared_state. What I understand from the code is that _shared_state is passed to the new objects' __dict__ attribute. So how is the state actually shared between instances when __dict__ is never passed to _shared_state?!