finding object using IS instead of ==

Geoff Gerrietts geoff at
Thu Aug 28 06:54:46 CEST 2003

Quoting Mark Hahn (mark at
> > If I have a large collection (list, tuple, or dict) of objects,
> > can I locate one quickly that matches a given object using the IS
> > equivalence operator instead of the value == operator?
> Clarification: Is there a FASTER way that takes advantage of the IS
> equivalence than using the available == method.  I assume the ==
> method does a linear search, except for a dict key lookup, which is
> not what I'm talking about.
> Obviously if two references are the same object (IS equivalent) then
> they are == also so you could find based on == and then check for
> IS, but I want something faster.

I'm not exactly sure how to answer your question. The short answer
might be "yes" but I can't produce a long answer because I'm not even
sure the short answer is right, for the question you're asking.

An example might help?

Let's say you have a large list of O objects L1:

  class O: 
    def __init__(self, oid):
      self.oid = oid

  L1 = [O(oid) for oid in range(50000)]

And somehow, you have a handle to one of those O objects:

  handle = L1[random.randint(0,49999)]

You can do a search to retrieve it (them) using 'is':

  matches = [o for o in L1 if o is handle]

But is this useful to your specific problem domain? That's harder to


Geoff Gerrietts             "That's it! I've had it with your sassy mouth!
<geoff at gerrietts net>     I didn't want to do this! (Well, actually,    I did....)"  -- Mojo Jojo, "Bubblevicious"

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