[Python-Dev] unsubscriptable vs object does not support indexing (original) (raw)

MRAB python at mrabarnett.plus.com
Thu Sep 24 02:15:19 CEST 2009

Janzert wrote:

Steven D'Aprano wrote:

On Thu, 24 Sep 2009 06:47:41 am Dino Viehland wrote:

So I am +1 on unified the message and +1 on using the "does not support indexing" one. I'd be +1 on the unified message as well - but it seems what that message should be may be contentious (and quite a bike shed discussion at that). The bug David linked to (http://bugs.python.org/issue5760) has a preference for subscript because that's what's used elsewhere in the language. For what it's worth, "unsubscriptable object" seems to me to be mysterious to many newbies, and even a few non-newbies. It took me something like seven years of coding to stop reading it as "unscriptable object", and I'm sure I won't be the only one. As far as I can see, in practice, people talk about obj[i] as the item at index i, not the item at subscript i -- the term "subscript" in this context seems to be rare to non-existent except for the error message.

How about if it's obj["item"]? To me the following makes complete sense, but then it seems that I may just be the odd one out. class A(object): ... pass ... a = A() a[1] Traceback (most recent call last): File "", line 1, in TypeError: 'A' object is unindexable a["a"] Traceback (most recent call last): File "", line 1, in TypeError: 'A' object is unsubscriptable I prefer "index" to "subscript" and "does not support foo" or "cannot be fooed" to "is unfooable" (because, to me, "not" is more explicit than "un-"). I also prefer the same term to be used irrespective of the value used.

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