[Python-Dev] relative import circular problem

Thu Apr 4 23:00:01 CEST 2013

On Thu, Apr 4, 2013 at 4:42 PM, Guido van Rossum <guido at 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... 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 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.) 