[merge] python 2.5 fixes

[John Arbash Meinel]

Aaron Bentley wrote:
> John Arbash Meinel wrote:
> 
>>> If you don't want to change the ElementTree sources (which I think we
>>> should, and contribute the changes upstream). I can modify
>>> 're.compile()' before importing elementtree, and then restore it afterwards.
> 
> Hmm.  Aren't a lot of our startup time issues due to regex compilation?
> 
> I wonder whether Python should make _sre.SRE_Pattern objects lazy?
> 
> Aaron

It isn't the only thing. "import bzrlib.errors" actually takes 3-6ms to
import, just because it is creating lots of classes. That said, it is
the #1 startup cost.

So even though regex compilation *is* expensive (it can take 25ms to
compile a single regex). There are other things which cost us time as well.

I'm hoping to move some of my 'lazy_import' fixes into bzr for 0.12, and
then after Registry gets merged, start splitting up our 'cmd-*' classes,
as well as our Branch & Repository formats.

Which should mean that in a default run, very little extra code needs to
get imported. I already have a lot of the lazy_import stuff done. But I
want to merge it early in a new cycle, rather than late. So that bzr.dev
gets a lot of pounding.

One problem with testing lazy import with out test suite, is that
basically our test suite imports *everything* so you don't notice import
dependency issues. Like the fact that just doing 'import
bzrlib.repository' fails because it imports bzrlib.revision_tree which
imports bzrlib.tree which imports bzrlib.revision_tree causing a
dependency cycle (because RevisionTree used to be defined in bzrlib.tree).

Which is technically deprecated, but since we don't have a way to force
a 'DependencyWarning' when accessing an object in the wrong module, I
don't think it is safe to remove it.

John
=:->

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