Checking for member existence in Python

Question

I regularly want to check if an object has a member or not. An example is the creation of a singleton in a function. For that purpose, you can use hasattr like

Answer 1

I have to agree with Chris. Remember, don't optimize until you actually need to do so. I really doubt checking for existence is going to be a bottleneck in any reasonable program.

I did see http://code.activestate.com/recipes/52558/ as a way to do this, too. Uncommented copy of that code ("spam" is just a random method the class interface has):

class Singleton:
    class __impl:
        def spam(self):
            return id(self)
    __instance = None
    def __init__(self):
        if Singleton.__instance is None:
            Singleton.__instance = Singleton.__impl()
        self.__dict__['_Singleton__instance'] = Singleton.__instance
    def __getattr__(self, attr):
        return getattr(self.__instance, attr)
    def __setattr__(self, attr, value):
        return setattr(self.__instance, attr, value)