[Python-Dev] Relative Package Imports

Jim Fulton jim@digicool.com
Mon, 13 Sep 1999 11:21:15 -0400

Gordon McMillan wrote:
> [relative package imports]
> [JimF]
> > > I'll second Marc-Andre here.
> > >
> > > A significant headache occurs when you have a package
> > > that has sub-packages.  Sub-packages need to be able to
> > > reference other sub-packages within the same package without
> > > knowing where the containing package is installed.
> [GvR]
> > You never need to know where it is installed.  When I said absolute
> > package name I meant package name (e.g. zope.foo.bar.subpack) not
> > filename.  As Tim has argued, the ability to change the name of the
> > toplevel here is a liability, not a feature.
> In between. I can see relative packages as *one* way of handling
> certain problems. Consider:
>  zope.Win32
>  zope.Unix
> with both of these having alternate implementations of  subpackages foo
> and bar. Then for (the current) foo.a to get to (the  current) bar.b,
> using a relative import seems a natural.

I wouldn't use relative imports for this.
> This can, of course, be done in pure Python. So can doing things  in
> zope.__init__.py that make the appropriate implementations of  foo and
> bar appear to be zope.foo and zope.bar. On any criteria I  can think of,
> this would be a superior solution. (*)

I agree. This is not a good motivating example for relative imports.
> What I am against is further complicating the already over  complicated
> built in import mechanism.

The current scheme doesn't seem all that complicated to me.
I wouldn't be in favor of making it more complicated if there wasn't
a good reason.  I think that, in working on the Zope framework, 
I've found some pretty good reasons for relative imports.

> (*) such as a zope.__init__.py that looks like this:
> import sys
> if sys.platform[:3] == 'win':
>   nm = __name__ + '.Win32'
> else:
>   nm = __name__ + '.Unix'
> new = __import__(nm)
> sys.modules[__name__] = sys.modules[nm]

Right, this would be silly. This is not a good example.


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