This is an old copy of the Python FAQ. The information here may be outdated.

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): = name

    def getinstances(cls):
        dead = set()
        for ref in cls._instances:
            obj = ref()
            if obj is not None:
                yield obj
        cls._instances -= dead

a = MyClass("a")
b = MyClass("b")
c = MyClass("c")

del b

for obj in MyClass.getinstances():
    print # 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):

However, since an application is likely to have thousands of active objects, this variant isn’t very efficient.

CATEGORY: programming


A Django site. rendered by a django application. hosted by webfaction.