一些小工具

tools.py

class Singleton(object):
    """ 单例类
    
    > @Singleton
    > class Demo:
    >     def __init__(self):
    >         pass
    >
    > assert Demo() == Demo()
    
    """
    def __init__(self, cls):
        self._cls = cls
        self._instance = {}

    def __call__(self, *args, **kwargs):
        if self._cls not in self._instance:
            self._instance[self._cls] = self._cls(*args, **kwargs)
        return self._instance[self._cls]