Bazaar-NG vs. Mercurial -- speed comparison

[John Arbash Meinel]

Bryan O'Sullivan wrote:
> John A Meinel <john <at> arbash-meinel.com> writes:

...

>> Bzr could be better about not having to load support for all of its
>> features until they are actually needed. 'hg' actually uses a solution
>> called 'demandload', which we probably could just move directly into the
>> bzr code.
> 
> You should grab it and use it.  It's very nice.  It imposes a one-time cost
> when an attribute of a demand-loaded symbol is looked up; after that, the
> importing namespace is patched with the real module, so there's no
> subsequent cost.
> 

Well, unfortunately it doesn't really do everything that you might want
it to do. It really only supports importing modules that way. So stuff like:
import bzrlib => demandload(globals(), 'bzrlib') works well.

But this syntax isn't supported at all:
import bzrlib.errors as errors

Though maybe you could do:
demandload(globals(), 'bzrlib:errors')
But that loads the 'errors' member of bzrlib, not the actual module.

In the meantime, I think this does the right thing:
demandload(globals(), 'bzrlib.errors')
errors = bzrlib.errors

Also, something like this:

from bzrlib.errors import (BzrError,
                           BzrCheckError,
                           BzrCommandError,
                           BzrOptionError,
                           NotBranchError)


looks like you would translate that into:
demandload(globals(), 'bzrlib.errors:BzrError,BzrCheckError,
                      'BzrCommandError,BzrOptionError,NotBranchError')

But that doesn't work, because demandload._replacer_from requires that
you access an attribute, and __call__ doesn't seem to count.

So I'll keep playing, but in the meantime it isn't just a drop-in
replacement.

John
=:->

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