Iterating over objects of a class

Scott David Daniels Scott.Daniels at Acm.Org
Wed Dec 24 20:48:57 CET 2008


Kottiyath wrote:
> ...
> Having a registry inside the class instance and looping through them
> was the only clean thing I could think of.
> I understand that garbage collection would be an issue - but is there
> any way out?

Search for weakref in the documentatione.
In this case, I'd use a WeakValueDictionary() from id(obj) to obj.
Note id(obj) is guaranteed to be unique for all objects in existance,
but the id of a collected object may match the id of a new object.

 >>> import weakref
 >>> d = weakref.WeakValueDictionary()
 >>> vs = [Int(n) for n in range(3, 500, 70)]
 >>> for n in vs:
	d[id(n)] = n
	v = Int(n+1)
	d[id(v)] = v
 >>> for obj in d.values(): # values is safer than itervalues
     print obj
 >>> # note the above was the following, which fails:
 >>> for v in d.values(): # values is safer than itervalues
     print v


For extra credit, explain why values is better.

--Scott David Daniels
Scott.Daniels at Acm.Org



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