Python packages - problems, pitfalls.
prabhu at aero.iitm.ernet.in
Sun Nov 4 07:37:50 CET 2001
Recently I discovered that there is some very unfortunate behaviour
with python packages.
Lets say I have a directory 'pkg' that is the root of a package.
Inside this directory I have a sub-package, called sub. So its
Now, from b I'd expect to be able to import 'a' straight away.
Say in b.py I do
This will not work! I know why it happens but shouldn't Python be
smart enough to avoid such problems? Why I consider this a major
problem is that the importing of a sub-package depends on where its
parent package is!! So if pkg is no longer the root of the package
and say its put inside another BigPkg then to make pkg's sub packages
work you'd have to edit *all* the sub packages and change every
reference to pkg.a to BigPkg.pkg.a. This is a huge pain.
One way around this is to do something like this inside sub's
This however will cause the module a to be loaded several times! Once
as pkg.a and once as pkg.sub.a!! Imagine what would happen if you had
many such sub-packages.
One way around this would be for import to see if the importee (the
(1) is in the same directory (no problem, this already works)
(2) is part of a the same package that the importer (the code that
does the import) belongs to. If so look in the parent packages
(3) Keep doing (2) untill you are out of all parent packages.
Something like walking a tree.
(4) If all this fails, search for modules in sys.path.
I did some prelimiary searching and came upon the import-sig which led
me on to imputil. I also found that knee.py does something to
eliminate such problems. However, I find that
(1) imputil isn't documented enough (at all?) and I can't really
find neat examples that illustrate its usage.
(2) I don't know if using imputil is recommended and what the
problems are with using it etc.
(3) knee.py warns me saying """ This code is intended to be read,
not executed. However, it does work -- all you need to do to enable
it is "import knee"."""
I know that I can experiment, read the source, grok it all and look
for solutions but at the moment don't have much time for it. I'd like
to know what you folks think.
Are there better ways to get around this packaging problem? Is this a
know problem that folks are working on?? Why is it that Python does
not deal with this issue more sensibly?
Prabhu Ramachandran MayaVi Data Visualizer
Where there's no emotion, there's no motive for violence.
-- Spock, "Dagger of the Mind", stardate 2715.1
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