Let's say I have an id of a Python object, which I retrieved by doing id(thing). How do I find thing again by the id number I was given?
views:
572answers:
5
+5
A:
You can use the gc module to get all the objects currently tracked by the Python garbage collector.
import gc
def objects_by_id(id_):
for obj in gc.get_objects():
if id(obj) == id_:
return obj
raise Exception("No found")
Manuel Ceron
2009-09-08 22:34:56
This has an aliasing issue: an ID obtained at an arbitrary point in the past may now refer to a different object.
chaos
2009-09-08 22:37:59
As long as you've maintained a reference to the object, that won't happen. Just the same, this is generally a bad idea.
Glenn Maynard
2009-09-08 23:16:53
I agree with many of the other commenters: don't do this. Make your own dictionary of objects.
Ned Batchelder
2009-09-09 11:26:23
+13
A:
Short answer, you can't.
Long answer, you can maintain a dict for mapping IDs to objects, or look the ID up by exhaustive search of gc.get_objects(), but this will create one of two problems: either the dict's reference will keep the object alive and prevent GC, or (if it's a WeakValue dict or you use gc.get_objects()) the ID may be deallocated and reused for a completely different object.
Basically, if you're trying to do this, you probably need to do something differently.
chaos
2009-09-08 22:37:30
I've been intending to throw away the id reference in the object's `__del__`, do you think that this will make sure things will not break?
cool-RR
2009-09-08 22:44:58
+1: Agree: Don't do this. Simply create a proper dictionary of objects with proper keys -- you'll be a lot happier.
S.Lott
2009-09-08 23:51:03
+1
A:
eGenix mxTools library does provide such a function, although marked as "expert-only": mx.Tools.makeref(id)
Fabian Neumann
2009-09-08 22:44:18
+4
A:
You'll probably want to consider implementing it another way. Are you aware of the weakref module?
(Edited) The Python weakref module lets you keep references, dictionary references, and proxies to objects without having those references count in the reference counter. They're like symbolic links.
Ken
2009-09-08 22:46:31
+1
A:
Just mentioning this module for completeness. This does what you want without looping throughout every object in existence. It will obviously crash if the object isn't there anymore.
Unknown
2009-09-09 05:01:52