Singleton in Python3

singleton.py

import threading

class ThreadingSingleton:
    _instance = None
    _lock = threading.Lock()

    def __init__(self):
        print('__init__')

    def __new__(cls):
        with cls._lock:
            if cls._instance is None:
                cls._instance = super().__new__(cls)
                cls._instance.init()

        return cls._instance

    def init(self):
        self.test = False
        print('init')

if __name__ == "__main__":
    t1 = ThreadingSingleton()
    t2 = ThreadingSingleton()

    print(t1.test)
    print(t2)
    print(t1)

Output

init
__init__
__init__
False
<main.ThreadingSingleton object at 0x7f52ccec9f98>
<main.ThreadingSingleton object at 0x7f52ccec9f98>

init called only once though __init__ called twice. So members of the class must be initialized in init, not __init__.
The last two lines of output shows t1 and t2 are the same instance.