Package organization

[Robert Ferrell]

Graham Ashton <gashton at cmedltd.com> wrote in message news:<pan.2003.11.19.10.06.02.882280 at cmedltd.com>...
> On Tue, 18 Nov 2003 16:38:15 -0800, Robert Ferrell wrote:
> 
> > I have a question about how to organize modules in a package.  I think
> > there is something fundamental that I am missing.  Say I'm creating a
> > package,
> > GreatPackage, which has three sub-packages, myUtilities, GoodStuff,
> > MoreGoodStuff.
> > 
> > The directories look like:
> > 
> > GreatPackage
> >      |
> >      |-- myUtilities
> >      |
> >      |-- GoodStuff
> >      |
> >      |-- MoreGoodStuff
> > 
> > What is the right way for modules in GoodStuff and MoreGoodStuff to
> > refer to modules etc... in myUtilities?
> 
> There's a PEP that recommends that when importing things you refer to them
> explicitly; i.e. inside GoodStuff you'd say 
> 
>   import GreatPackage.myUtilities
> 
> rather than just 
> 
>   import myUtilities
> 
> I've only benefitted from doing it that way myself in large apps that have
> had many packages with sub packages. It keeps you safe from module name
> clashes at different levels of the hierarchy (not that I think they're a
> sensible thing to have). By name clashes I mean if you have modules
> set up like this:
> 
>   lib
>   shoe.lib
>   shoe.fruit
> 
> then you can't get at the top level lib module from inside shoe.fruit.
> 
> > from GreatPackage.myUtilities import aUtilityThingy
> > 
> > in a module in GoodStuff, then the whole package gets loaded,
> > including MoreGoodStuff.
> 
> MoreGoodStuff won't get loaded if you import GreatPackage, unless
> GreatPackage/__init__.py causes it to be loaded. Obviously, if something
> in myUtilities imports something from MoreGoodStuff then python will
> attempt to load MoreGoodStuff when importing myUtilities.


Ah Ha!  Somehow I'd convinced myself that GreatPackage/__init__.py had
to import all the submodules.  So that's what I was doing.  That's
obviously wrong.  Now that I've corrected that mistake I see that what
I was having trouble with is not an issue.

> Also, because you're importing something from inside a module using the
> "from" style imports you're risking running into circular reference
> problems. In my experience from imports are best avoided, unless you're
> importing a module from a package.

I don't understand this comment.  How does "from" style importing
increase the risk of circular imports?

Thanks for the clarification!
-robert