使Daniel Brodie&ŧ039；的单例配方使用关键字参数

Posted 2021-02-27

The ASPN cookbook has many recipes for singletons in Python. So far, this one
http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/412551
has been my favourite, because it is so simple and concise. However, I just ran into a brick wall when I tried to use it with a class that can be initialized with keyword arguments. This is my first draft for a solution to this problem. It's quick and dirty; please give it a glance and leave a comment if you find a problem.

class Singleton(type):
    def __init__(self, *args, **kwds):
        type.__init__(self, *args, **kwds)
        self._instances = {}
 
    def __call__(self, *args, **kwds):
        sig = args + tuple(sorted(kwds.items()))
        if not sig in self._instances:
            self._instances[sig] = type.__call__(self, *args, **kwds)
        return self._instances[sig]