[Python-3000] Spooky behavior of dict.items() and friends

[David Pokorny]

On Tue, Apr 1, 2008 at 4:40 PM, Guido van Rossum <guido at python.org> wrote:
> I'm not sure that it's really a safe vs. non-safe issue. The OP's
>  concern is that the change affects behavior of keys() and friends that
>  people have internalized for the past 18 years. I certainly don't see
>  this is a reason to change it back (we knew this would be the case). I
>  do think it needs to be ephasized in every "What's New" doc. It's
>  already in the list of Common Stumbling Blocks, but the paragraph
>  there could be expanded a bit.

I agree that the 3.0 behavior is safe but surprising.

So unless I am misinterpreting this, it sounds like the burden of
proof now falls on the option to keep the status quo. The thing is
that it seems to me that if that an outside observer were to look at
this situation, then they might ask why the names are being changed
when the current behavior is functional and no one is clamoring for
the change.

If you disagree, then I still don't understand the motivation on the
PEP, and the current motivation, "being able to do set operations on
keys and items without having to copy them" does not appear to pertain
to the issue of which names should correspond to which behavior. Once
viewitems() or itemview() gets backported to 2.6, then unless I am
missing something, the PEP is concerned solely with changing the
names.

FWIW, there is a distinction between "loud" changes such as, say,
"print" changing from a function to a statement or "except" blocks
rejecting the "except TypeError, exc" syntax in favor of "except
TypeError as exc" and "silent" changes such as the one under
discussion; the change under discussion alters the meaning of an
expression that is valid in both 2 and 3 whereas in the other cases
the code will not compile in 3.

David