http://bugs.python.org/issue17636
On Thu, Apr 4, 2013 at 8:03 PM, Brett Cannon <br...@python.org> wrote: > > 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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