On 4/14/2014 1:19 PM, Guido van Rossum wrote:
Some quick thoughts:
- I'd prefer a name that plays on 2 and 3, not 2 and 8. :-)
- Are you sure this isn't better directed to python-ideas first? Most
ideas have to prove their worth in that list before python-dev will give
them the light of day.
- When it comes to purely syntactic issues (e.g. "except x, y:") a
linter or some other separate tool can handle this well (heck, you can
build it into an import hook probably :-).
- When it's about backported modules, a sumo distribution is probably
the way to go; when it's about renamed stdlib modules, six (perhaps an
extended version) should cover you.
- Regarding warning about the changed dict API, I wonder how you plan to
implement that if you allow passing dict object back and forth between
code that has opted in to single-source and code that hasn't yet. Please
think through some specific examples before responding.
- But the biggest issue is of course bytes vs. text. You would have to
first do a careful analysis of the *whole* problem before you can even
think about proposing a solution. Too many people think their is an easy
solution for this; but almost everybody is focused on only part of the
problem (the part that causes them immediate pain) without realizing
that other people's pain may be different.
- As far as your assertion that it would have to come from python-dev
because nobody outside is going to tackle it, I think it's the opposite:
the core developers would prefer not to have to deal with this, while
some folks outside the inner circles will not be discouraged by our
opinions (e.g. Stackless is working on "Stackless 2.8").
- Regarding open source projects having a reputation of "not taking
contributions", I would guess that this is usually about those
"contributions" violating the most basic rules of the project (and I
don't mean the coding style). I do want to discourage discussions with
Did you mean 'don't want to discourage'?
users like the company you referred to, but I think it would be much
more useful if they laid out their problems for us instead of expecting
they can buy acceptance for a "solution" they develop in-house. We could
then hopefully have a productive dialog over many months where we
iterate over possible approaches that could be acceptable both to Python
and to the customer. But it will take a significant investment of time
on both sides -- there is no shortcut. And it's not a particularly
interesting problem (for most people) to work on -- things like
designing a notation for optional type declarations are always much more
fun. :-)
On Mon, Apr 14, 2014 at 11:32 AM, Steve Dower <steve.do...@microsoft.com
<mailto:steve.do...@microsoft.com>> wrote:
Just in case there's anyone out there who isn't yet sick of
discussing how to proceed with Python 2.7, I have some more inputs
to contribute.
To put it up front, I'm totally against "CPython 2.8" ever becoming
a real thing. Anything that comes out should be seen as a migration
path, not an upgrade path. I'll also admit I'm not heavily invested
in working on it myself, but I had a number of conversations during
PyCon (as well as being at the language summit) that puts me in a
position to share the ideas and concerns that have been raised.
The main trigger was a conversation I had with two employees of a
very large bank that has about 3000 Python users (not developers -
mostly financial analysts) and 16 million lines of code running on
2.7. They are keen to migrate to 3.x but cannot afford to stop work
entirely while their code is updated. (There was much more to the
conversation than I'm relating here - I'm keeping to the directly
relevant bits.)
In describing the approach they'd like to take, they made me realise
that there is definitely a place for a Python that is different but
mostly compatible with 2.7, in a way that 2.7.x could not be. For
the sake of having a name, I'll refer to this as "Python 2migr8"
(pronounced "to migrate" :) ).
The two important components of Python 2migr8 would be the ability
to disable 2.7-only features, and to do so on a module-by-module basis.
My best idea so far would be to have a magic comment (to ensure 2.7
compatibility better than a "from __future__ ...") near the top of
the file that marks that file as "must straddle 2.7 and 3.3". Adding
this comment causes (for example) the parser to treat "except x, y"
as a syntax error in this file, forces "from __future__ import ...",
hides "dict.iterkeys", undefines "basestring", etc., but only for
this file. (I haven't thought through all the possibilities or
implications - Eric Snow said he was going to sprint on this
today/tomorrow, so he'll soon have a better idea just what can be done.)
In effect, 2migr8 would be the version that *only* supports
"single-source" files. This allows large code bases to progressively
migrate modules from 2.x to single-source while continuing to run
against Python 2.7. As files are updated, they are marked as being
single-source. When all files have this marker, it should be
possible to flip the switch and run with Python 3.3 or later.
You could also think of this as enabling "-3 --warnings-as-errors"
for individual modules, though since the user has already opted in
to 2migr8, it isn't unreasonable to make more significant changes,
like having dict.keys returning a list that warns if it is mutated.
This sort of warning can only really be done by changing the
interpreter - static analysis just can't catch everything - and only
when users accept a potential performance hit and low probability of
breakage when they move to 2migr8 (followed by a not-quite-as-low
probability of breaking when they eventually move from 2migr8 to
3.x, but it's still better than guaranteed breakage).
As a fork, it would also be possible to bundle the modules that have
been backported, and possibly also to disallow importing deprecated
stdlib modules when 2.7 functionality is disabled. As I said, I
haven't thought through all the possibilities, but the general idea
is to take 2.7 and *remove* features so it becomes easier to migrate.
Where does python-dev come in? Obviously this is where a fork like
this would have to start - there has been such strong and public
opposition to any significant changes like this that you'd be hard
pressed to find someone willing to start and promote it from
outside. There is also a good opportunity to make a start and
directly invite those using it to contribute the rules or warnings
that they need - the 3000 Python "users" I mentioned earlier are
backed by a team of true developers who are more than capable of
contributing, and this would be a great opportunity to directly
invite them. However unfair and incorrect it may be, there is a
perception in some businesses that open-source projects do not want
contributions from them. I invited more than one business to have
someone join python-dev and get involved during PyCon, and I heard
that others did the same - it may not be at the level of employing a
core developer full time, but it's the starting point that some
companies will ne
ed to be able to become comfortable with employing a core dev.
I'm not pretending to have a full plan on how this will work. I was
privileged to have some private conversations during PyCon that are
directly relevant, so I'm bringing it here to promote the
discussion. Thanks to everyone I had a chance to chat to, and to
everyone generally for a great PyCon.
Cheers,
Steve
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--
--Guido van Rossum (python.org/~guido <http://python.org/~guido>)
--
Terry Jan Reedy
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