On Apr 4, 2013 6:47 PM, "Guido van Rossum" <gu...@python.org> wrote: > > +1 on Brett and PJE just doing this.
I'll file a bug when I get home. -brett > > On Thu, Apr 4, 2013 at 3:38 PM, Brett Cannon <br...@python.org> wrote: > > > > > > > > On Thu, Apr 4, 2013 at 5:00 PM, PJ Eby <p...@telecommunity.com> wrote: > >> > >> On Thu, Apr 4, 2013 at 4:42 PM, Guido van Rossum <gu...@python.org> wrote: > >> > I do think it would be fine if "from a import b" returned the > >> > attribute 'b' of module 'a' if it exists, and otherwise look for > >> > module 'a.b' in sys.modules. > >> > >> Technically, it already does that -- but inside of __import__, not in > >> the IMPORT_FROM opcode. > >> > >> But then *after* doing that check-and-fallback, __import__ doesn't > >> assign a.b, because it assumes the recursive import it called has > >> already done this... > > > > > > It's an unfortunate side-effect of having loaders set sys.modules for new > > modules not also set them as an attribute on their parent package > > immediately as well (or you could argue it's a side-effect of not passing in > > a module instead of a name to load_module() but that's another discussion). > > > >> > >> which means that when __import__ returns, the > >> IMPORT_FROM opcode tries and fails to do the getattr. > >> > >> This could be fixed in one of two ways. Either: > >> > >> 1. Change importlib._bootstrap._handle_fromlist() to set a.b if it > >> successfully imports 'a.b' (inside its duplicate handling for what > >> IMPORT_FROM does), or > > > > > > It's three lines, one of which is 'else:'. Just did it. > > > >> > >> 2. Change the IMPORT_FROM opcode to handle the fallback itself > >> > >> > >> While the latter involves a bit of C coding, it has fewer potential > >> side-effects on the import system as a whole, and simply ensures that > >> if "import" would succeed, then so would "from...import" targeting the > >> same module. > >> > >> (There might be other fixes I haven't thought of, but really, changing > >> IMPORT_FROM to fallback to a sys.modules check is probably by far the > >> least-invasive way to handle it.) > > > > > > This is my preference as well. The change would be small: I think all you > > need to do is if the getattr() fails then fall back to sys.modules. Although > > if it were me and I was casting backwards-compatibility to the wind I would > > rip out the whole fromlist part of __import__() and let the bytecode worry > > about the fromlist, basically making the import opcode call > > importlib.import_module(). > > > > > > -- > --Guido van Rossum (python.org/~guido)
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