[Import-SIG] PEP 420: Implicit Namespace Packages

[Antoine Pitrou]

On Sat, 5 May 2012 16:27:26 +1000
Nick Coghlan <ncoghlan at gmail.com> wrote:
> On Sat, May 5, 2012 at 8:47 AM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> > Unless there are clear advantages over PEP 382, I'm -1 on this PEP, and
> > would like to see PEP 382 revived.
> 
> I raised this question as well, and the PEP as written doesn't do a
> great job of summarising the thread that addressed it.
> 
> There were two counterpoints raised that I found compelling:
> 
> A. Guido simply doesn't like directory extensions. I have to agree
> with him that using them to handle packaging would be a weird and
> unusual approach, and, well, he *does* get to play the BDFL card in
> cases like this.

Well, I agree that "foo.pyp" isn't very pretty, but that's a pretty
minor argument. At least it's explicit.
(of course, another marker could have been chosen: for example
an empty "foo/__namespace__.py", or whatever else floats our
boat of aesthetics)

> B. Current version control systems are still pretty abysmal when it
> comes to coping with directory renames, and we want to avoid
> unnecessary stumbling blocks on the migration path from the current
> pkgutil.extend_path() based namespace packages to the new native
> system.

Isn't that baseless? AFAIU all modern DVCS should cope correctly with
a directory rename. Even SVN may be ok.

If anything, I'd like to see data points about these "current version
control systems" being "pretty abysmal [!] when it comes to coping
with directory renames".

(preferably something else than a 2007 rant by Mark Shuttleworth in
order to justify bzr's existence :-))

> The extra step required by the PEP 382 approach is exactly the kind of
> pointless revision history noise that PEP 414's reintroduction of
> explicit Unicode literals is designed to eliminate from Python 2 to
> Python 3 migrations.

Except that noone *has* to migrate to namespace packages. These are
fairly rare and only useful for a couple of big projects.
(I've only heard about Zope using them; Twisted AFAICT doesn't)

Even then, renaming a directory is hardly comparable to the hurdle of
migrating unicode literals from Python 2 to Python 3. The analogy
sounds melodramatic.

> Between "Guido doesn't like directory suffixes" and "version control
> systems are still fairly bad at handling directory renames", I changed
> my own opinion on PEP 420 from -1 to +0.

This doesn't address PEP 420's issues, which will still come to bite us
in 10 years: the potential for confusion, the weirdness of the lookup
algorithm.

> If we'd been starting from a
> clean slate with no language history or migration of existing projects
> to account for, then my opinion would be different, but given where we
> are today, I find the pragmatic argument in favour of simply losing
> the explicit markers compelling.

The real pragmatic argument would be to avoid creating maintenance and
support issues for the future, IMO.

Regards

Antoine.