[Python-Dev] iter.index() (original) (raw)

Bob Ippolito bob at redivi.com
Sun Apr 18 22:50:13 EDT 2004

On Apr 18, 2004, at 10:21 PM, Christian Stork wrote:

On Sun, Apr 18, 2004 at 10:08:25PM -0400, Bob Ippolito wrote:

On Apr 18, 2004, at 9:53 PM, Christian Stork wrote:

Hi,

I wanted to do something like i = itertools.chain(list1, list2).index(elem) but that gave me ... AttributeError: 'itertools.chain' object has no attribute 'index' If I use the operator module it works just fine. i = operator.indexOf(itertools.chain(list1, list2), elem) Why not add the index method to iterator objects? Of course, internally only next() is used by the default implementation. An iterator mutates each time you call its next(). Your call to indexOf does one of three things: exhaust some of your iterator and return a useless integer, Why useless? It returns the index. Why do I have to build a new concatinated list (or my own special index function) in order to get that information?

It returns an index into some sequence that no longer exists. What good is that?

exhaust all of your iterator and raise an exception, Yep, just as it would for lists.

The difference is that the iterator's life is more or less over, there's probably nothing useful you can do with it, but a list is not changed by this operation.

If you want an object that acts like a list, you should use a list. I don't see anything inherently "listy" about index(). It just counts how many elements there are to reach elem. And obviously the functionality is already there in the operator module. I'm just proposing a little convenience.

I think it's pretty rare that you would want to know this information at the cost of exhausting some/all of your iterator... and if that really is what you want, then you should just use operator.indexOf.
There are MANY iterable types, it's not reasonable to change them all.

-bob

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