Open Stack

So this change came in with adding glance.store -
https://review.openstack.org/#/c/115265/5/lib/glance, which I think is a
bad direction to be headed.

Here is the problem when it comes to working with code from git, in
python, that uses namespaces, it's kind of a hack that violates the
principle of least surprise.

For instance:

cd /opt/stack/oslo.vmware
pip install .
cd /opt/stack/olso.config
pip install -e .
python -m olso.vmware
/usr/bin/python: No module named olso.vmware

In python 2.7 (using pip) namespaces are a bolt on because of the way
importing modules works. And depending on how you install things in a
namespace will overwrite the base __init__.py for the top level part of
the namespace in such a way that you can't get access to the submodules.

It's well known, and every conversation with dstuft that I've had in the
past was "don't use namespaces".

A big reason we see this a lot is due to the fact that devstack does
'editable' pip installs for most things, because the point is it's a
development environment, and you should be able to change code, and see
if live without having to go through the install step again.

If people remember the constant issues with oslo.config in unit tests 9
months ago, this was because of mismatch of editable vs. non editable
libraries in the system and virtualenvs. This took months to get to a
consistent workaround.

The *workaround* that was done is we just gave up on installing olso
libs in a development friendly way. I don't consider that a solution,
it's a work around. But it has some big implications for the usefulness
of the development environment. It also definitely violates the
principle of least surprise, as changes to oslo.messaging in a devstack
env don't immediately apply, you have to reinstall olso.messaging to get
them to take.

If this is just oslo, that's one thing (and still something I think
should be revisted, because when the maintainer of pip says "don't do
this" I'm inclined to go by that). But this change aims to start brining
this pattern into other projects. Realistically I'm quite concerned that
this will trigger more work arounds and confusion.

It also means, for instance, that once we are in a namespace we can
never decide to install some of the namespace from pypi and some of it
from git editable (because it's a part that's under more interesting
rapid development).

So I'd like us to revisit using a namespace for glance, and honestly,
for other places in OpenStack, because these kinds of violations of the
principle of least surprise is something that I'd like us to be actively
minimizing.

	-Sean

-- 
Sean Dague
http://dague.net