pythonic singleton class

singleton.py

class ClassName:
    _instance = None

    def __init__(self, arg1, arg2, arg3):
        if ClassName._instance is None:
            # do initialization here
            ClassName._instance = self

    def __new__(cls, **kwargs):
        if cls._instance is None:
            _instance = super().__new__(cls, **kwargs)
        else:
            _instance = cls._instance
        return _instance