[Distutils] Expectations on how pip needs to change for Python 3.4

Nick Coghlan ncoghlan at gmail.com
Sun Jul 14 12:41:31 CEST 2013

On 14 Jul 2013 18:24, "Noah Kantrowitz" <noah at coderanger.net> wrote:
> On Jul 14, 2013, at 12:35 AM, Nick Coghlan wrote:
> > On 14 July 2013 17:13, Donald Stufft <donald at stufft.io> wrote:
> > I think it would be reasonable for the pip maintainers to be asked to
declare a public API (even if that's "None") using the naming scheme or an
import warning and declare a backwards compatibility policy for pip itself
so that people can know what to expect from pip. I do not however, believe
it is reasonable to bind pip to the same policy that CPython uses nor the
same schedule. (If you weren't suggesting that I apologize).
> >
> > The main elements of CPython's backwards compatibility policy that I
consider relevant are:
> >
> > * Use leading underscores to denote private APIs with no backwards
compatibility guarantees
> > * Be conservative with deprecating public APIs that aren't
fundamentally broken
> > * Use DeprecationWarning to give at least one (pip) release notice of
an upcoming backwards incompatible change
> >
> > We *are* sometimes quite aggressive with deprecation and removal even
in the standard library - we removed contextlib.nested from Python 3.2 as a
problematic bug magnet well before I came up with the contextlib.ExitStack
API as a less error prone replacement in Python 3.3. It's only when it
comes to core syntax and builtin behaviour that we're likely to hit issues
that simply don't have a sensible deprecation strategy, so we decide we
have to live with them indefinitely.
> >
> > That said, I think the answer to this discussion also affects the
answer to whether or not CPython maintenance releases should update to
newer versions of pip: if pip chooses to adopt a faster deprecation cycle
than CPython, then our maintenance releases shouldn't bundle updated
versions. Instead, they should follow the policy:
> >
> > * if this is a new major release, or the first maintenance release to
bundle pip, bundle the latest available version of pip
> > * otherwise, bundle the same version of pip as the previous release
> >
> > This would mean we'd be asking the pip team to help out by providing
security releases for the bundled version, so we can get that without
breaking the public API that's available by default.
> >
> > On the other hand, if the pip team are willing to use long deprecation
cycles then we can just bundle the updated versions and not worry about
security releases (I'd prefer that, but it only works if the pip team are
willing to put up with keeping old APIs around for a couple of years before
killing them off once the affected CPython branches go into security fix
only mode).
> If I can surmise your worry here, it is that people will open an
interactive terminal, import pip, reflect out the classes/methods/etc, see
that despite being mentioned no-where in the Python or pip documentation
the methods and classes don't start with an underscore, and thus conclude
that this is a stable API to build against? I agree that conventions are
good, but I have to say this sounds like a bit of a stretch and certainly
anyone complaining that their undocumented API that they only found via
reflection (or reading the pip source) was broken basically gets what they
deserve. The point I was trying to make is that a major shift in thinking
is needed here. pip is not part of CPython, regardless of this bundling
neither this mailing list nor the CPython team will have any control (aside
from the nuclear option that the CPython team can elect to stop bundling
pip). If you think it would be good for the code-health of pip to be
clearer about what their public API is, I will suppor
>  t that all the way and in fact have an open ticket against pip to that
effect already, but that is something for the pip team to decide. This does
very much mean that the CPython team is not just backing the pip codebase,
but the PyPA/pip team. I think the past few years have shown them deserving
of this trust, and they should be allowed to run things as they see fit.
These lines get blurry since several people move back and forth between
CPython and PyPA (and distutils and PyPI, etc) hats, so I think this must
be stated clearly up front that what the CPython team thinks is
"reasonable" for an API policy will be nothing more than a recommendation
from very knowledgable colleagues and will be given the appropriate
consideration and respect it deserves based on that. Hopefully that makes
my point-of-view a little clearer.

I started a thread on python-dev proposing strengthened wording in PEP 8
regarding marking of private interfaces, but beyond that, yes, I now agree
that this isn't a blocker for bundling pip with CPython.


> --Noah
> _______________________________________________
> Distutils-SIG maillist  -  Distutils-SIG at python.org
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