Issue 3754 - Initial setup of the python-abp repo.

abp/__init__.py

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+__import__('pkg_resources').declare_namespace(__name__)

[Sebastian Noack, 2016/03/15 12:18:07]

I rarely used that stuff. So what is the benefit/purpose of declaring a
namespace with pkg_resources?

Also any reason you hide the import while it's not even optional?

[Vasily Kuznetsov, 2016/03/15 13:14:35]

This is needed in case we would have two separate python packages that contain
modules in abp namespace and they would be installed with easy_install. For
example if we have "python-abp" that contains abp.filters and "python-abp-foo"
that contains abp.foo. Easy_install would put them into two separate eggs and
then if we "import abp.foo" it would only search the first one and perhaps not
find "abp.foo".

Here's an example of this made just to demonstrate how it works:
https://github.com/kvas-it/test-namespace-pkg

Clearly, at the moment we don't need to worry about all of this, but not
declaring the namespace carries the danger that if in the future we introduce
python-abp-foo (maybe not with this name) then if people just "easy_install
python-abp-foo" on top of existing setup with python-abp, they will find that
"import abp.foo" mysteriously does not work and they need to update python-abp
to fix it (assuming that we have released a new version which declares the
namespace by that time). This is ugly.

Now one can argue that this is all very hypothetical and perhaps people should
not be using easy_install in the first place (pip handles the situation
correctly without the namespace declaration) but declaring the namespace is not
a big deal and I've never seen a python installation where the slowdown from it
would be significant. So my usual choice is: just declare the namespace, forget
about it and sleep well at night.

As for using __import__ instead of "import pkg_resources" -- it makes the whole
thing a neat one-liner which is one fewer line of meaningless code, whose only
purpose is to fix this glitch of python module system. So basically the reason
is purely cosmetic.

[Sebastian Noack, 2016/03/15 16:33:00]

FWIW, I would rather ignore that scenario, for reasons you already mentioned:

1. We don't need to bother until we will bundle partial packages.
2. If we do we can still add a namespace declaration here.
3. Nobody is (or should) use easy_install nowadays anyway and pip doesn't seem
to require namespace declarations.

That is not about performance, but about unnecessary code. So people that try to
understand what the code in this repo does will stumble upon this piece, and
might wonder similarly than I did what that is about.

Anyway, it's not a too important detail, to argue about it. So if you insist
keep it in there, but using __import__ magic just to avoid an additional line of
code, doesn't sound like a good practice. Also it probably would make sense to
make the dependency on pkg_resources optional.