How do I get a list of all instances of a given class?
Python does not keep track of all instances of a class (or of a built-in type), so if you need this functionality, you have to implement it yourself. One way to do it is to store a weak reference to each instance in class attribute. Here’s an example:
import weakref class MyClass: _instances = set() def __init__(self, name): self.name = name self._instances.add(weakref.ref(self)) @classmethod def getinstances(cls): dead = set() for ref in cls._instances: obj = ref() if obj is not None: yield obj else: dead.add(ref) cls._instances -= dead a = MyClass("a") b = MyClass("b") c = MyClass("c") del b for obj in MyClass.getinstances(): print obj.name # prints 'a' and 'c'
An simpler, brute-force approach is to ask the gc module for a list of all known objects, and filter out the objects that belong to the relevant class:
import gc for obj in gc.get_objects(): if isinstance(obj, MyClass): print obj.name
However, since an application is likely to have thousands of active objects, this variant isn’t very efficient.