Python单例模式的实现（基于__new__方法）

class Solution:
    # @return: The same instance of this class every time
    import threading
    _instance_lock = threading.Lock()
    
    @classmethod
    def getInstance(cls):
        if not hasattr(cls, '_instance'):
            with cls._instance_lock:
                cls._instance = object.__new__(cls)
        return cls._instance