[Python-Dev] folding cElementTree behind ElementTree in 3.3

[Nick Coghlan]

On Wed, Feb 22, 2012 at 8:16 AM, Andrew McNabb <amcnabb at mcnabbs.org> wrote:
> So, I would be one of those people who would flood in the complaints. :)

As another "you don't know what you're going to break" war story:

In Python 2.5, using "-m" with a package appeared to work, but
actually slightly corrupted the import state (mostly in a benign way,
but if it ever bit you it would lead to some very confusing
behaviour).

Since I'd never intended to allow that to happen (as I knew about the
state corruption problem), for 2.6 I added back the "this doesn't work
properly" guard that had been present in the earlier versions of 2.5,
but had been lost when some duplicate code in pkgutil and runpy was
merged into a single version.

Doing that broke things: http://bugs.python.org/issue4195

The basic rule is, if it's documented to work a certain way and the
current implementation does work that way, then, someone, somewhere is
relying on it working as documented. If it *doesn't* actually work
that way (or the behaviour isn't explicitly documented at all), then
we have some leeway to decide whether to bring the docs in line with
the actual behaviour or vice-versa. For the Element case though,
there's no such discrepancy - the docs and implementation have been
consistent for years, so we need to maintain the current behaviour if
the C acceleration is going to be used implicitly.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia