[Python-Dev] PEP 420 - dynamic path computation is missing rationale (original) (raw)

PJ Eby pje at telecommunity.com
Wed May 23 17:13:01 CEST 2012

On May 23, 2012 9:02 AM, "Nick Coghlan" <ncoghlan at gmail.com> wrote:

On Wed, May 23, 2012 at 10:31 PM, Eric V. Smith <eric at trueblade.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.findmodule 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 = importmodule(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 findmodule(), 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.) -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20120523/a47022aa/attachment.html>

More information about the Python-Dev mailing list