On May 23, 2012 9:02 AM, "Nick Coghlan" <firstname.lastname@example.org> wrote:
> On Wed, May 23, 2012 at 10:31 PM, Eric V. Smith <email@example.com> wrote:
> > On 05/22/2012 09:49 PM, PJ Eby wrote:
> >> It shouldn't - all you should need is to use
> >> getattr(sys.modules[self.modname], self.attr) instead of referencing a
> >> parent path object directly.
> > The problem isn't the lookup, it's coming up with self.modname and
> > self.attr. As it currently stands, PathFinder.find_module is given the
> > parent path, not the module name and attribute name used to look up the
> > parent path using sys.modules and getattr.
> Right, that's what PJE and I were discussing. Instead of passing in
> the path object directly, you can instead pass an object that *lazily*
> retrieves the path object in its __iter__ method:
> class LazyIterable:
> """On iteration, retrieves a reference to a named iterable and
> returns an iterator over that iterable"""
> def __init__(self, modname, attribute):
> self.modname = modname
> self.attribute = attribute
> def __iter__(self):
> mod = import_module(self.modname) # Will almost always get
> a hit directly in sys.modules
> return iter(getattr(mod, self.attribute)
> Where importlib currently passes None or sys.path as the path argument
> to find_module(), instead pass "LazyIterable('sys', 'path')" and where
> it currently passes package.__path__, instead pass
> "LazyIterable(package.__name__, '__path__')".
> The existing for loop iteration and tuple() calls should then take
> care of the lazy lookup automatically.
> That way, the only code that needs to know the values of modname and
> attribute is the code that already has access to those values.
Perhaps calling it a ModulePath instead of a LazyIterable would be better?
Also, this is technically a change from PEP 302, which says the actual sys.path or __path__ are passed to find_module(). I'm not sure whether any find_module() code ever written actually *cares* about this, though. (Especially if, as I believe I understand in this context, we're only talking about meta-importers.)