Antoine Pitrou wrote (on python-dev):
On Fri, 18 Apr 2014 22:31:29 -0400 Nick Coghlan <ncoghlan at gmail.com> wrote:
After spending some time talking to the folks at the PyCon Twisted sprints, they persuaded me that adding back the iterkeys/values/items methods for mapping objects would be a nice way to eliminate a key porting hassle for them (and likely others), without significantly increasing the complexity of Python 3. I'm -1 on this. This is destroying the simplification effort of the dict API in Python 3.
I'm one of the masses who basically ignores py3 in favour of py2.7 (or
2.6 or even 2.4...) because the code I write has to run on old python.
And even if I /want/ to be compatible with py3, the only way I can do
that is by doing things that perform poorly in the version of python
I'll actually be using in production, or by having ugly special cases
and boiler plate all over the place. Things like this really are a
barrier to adoption for py3...
There's already a "from __future__ ..." mechanism to help with
backwards incompatible changes (creating new keywords and syntax in
particular). But that only helps people stay on old versions of
python.
So why not create the opposite: "from __history__ import ..." that
allows you to use obsoleted ways of programming with new versions of
python? If you want to use iter* on dicts in py3.5, require a "from
__history__ import dict_iter" statement at the top of the file.
For py2.7, there is no __history__ module, but it's easy to add one to
your project that just says "dict_iter = True" to let the import
statement succeed. In general (looking forward to py4?) you could (at
least in theory) have "from __history__ import FOO" be a noop if FOO
is unknown, add support for whatever historical practice if it's known
and a barrier to adoption, and have it be a syntax error when it's
finally no longer supported at all. That way you only need to actually
define a symbol via the __history__ module when you're actually
removing an obsolete idiom from the language.
Cheers,
aj
--
Anthony Towns