On Tue, May 22, 2012 at 9:58 PM, Nick Coghlan <ncoghlan@gmail.com> wrote:
If you wanted to do this without changing the sys.meta_path hook API, you'd have to pass an object to find_module() that did the dynamic lookup of the value in obj.__iter__. Something like:
class _LazyPath: def __init__(self, modname, attribute): self.modname = modname self.attribute = attribute def __iter__(self): return iter(getattr(sys.module[self.modname], self.attribute))
A potentially cleaner alternative to consider is tweaking the find_loader API spec so that it gets used at the meta path level as well as at the path hooks level and is handed a *callable* that dynamically retrieves the path rather than a direct reference to the path itself.
The full signature of find_loader would then become:
def find_loader(fullname, get_path=None): # fullname as for find_module # When get_path is None, it means the finder is being called as a path hook and # should use the specific path entry passed to __init__ # In this case, namespace package portions are returned as (None, portions) # Otherwise, the finder is being called as a meta_path hook and get_path() will return the relevant path # Any namespace packages are then returned as (loader, portions)
There are two major consequences of this latter approach: - the PEP 302 find_module API would now be a purely legacy interface for both the meta_path and path_hooks, used only if find_loader is not defined - it becomes trivial to tell whether a particular name references a package or not *without* needing to load it first: find_loader() returns a non-empty iterable for the list of portions
That second consequence is rather appealing: it means you'd be able to implement an almost complete walk of a package hierarchy *without* having to import anything (although you would miss old-style namespace packages and any other packages that alter their own __path__ in __init__, so you may still want to load packages to make sure you found everything. You could definitively answer the "is this a package or not?" question without running any code, though).
The first consequence is also appealing, since the find_module() name is more than a little misleading. The "find_module" name strongly suggests that the method is expected to return a module object, and that's just wrong - you actually find a loader, then you use that to load the module.
While I see no problem with cleaning up the interface, I'm kind of lost as to the point of making a get_path callable, vs. just using the iterable interface you sketched. Python has iterables, so why add a call to get the iterable, when iter() or a straight "for" loop will do effectively the same thing?