how to get list of all instance in class python

1import weakref
2
3class MyClass:
4
5    _instances = set()
6
7    def __init__(self, name):
8        self.name = name
9        self._instances.add(weakref.ref(self))
10
11    @classmethod
12    def getinstances(cls):
13        dead = set()
14        for ref in cls._instances:
15            obj = ref()
16            if obj is not None:
17                yield obj
18            else:
19                dead.add(ref)
20        cls._instances -= dead
21
22a = MyClass("a")
23b = MyClass("b")
24c = MyClass("c")
25
26del b
27
28for obj in MyClass.getinstances():
29    print obj.name # prints 'a' and 'c'