On Sat, Jul 21, 2012 at 2:53 PM, Dave Angel <d...@davea.name> wrote: > On 07/21/2012 04:36 PM, Bruce Sherwood wrote: >> Thanks much for this clear statement. I hadn't managed to find any >> documentation on this specific issue. >> >> Bruce Sherwood >> >> On Sat, Jul 21, 2012 at 10:26 AM, Dave Angel <d...@davea.name> wrote: >>> Two of the things you mustn't do during an import: >>> >>> 1) start or end any threads >>> 2) import something that's already in the chain of pending imports. >>> (otherwise known as recursive imports, or import loop). And there's a >>> special whammy reserved for those who import the script as though it >>> were a module. >>> >>> Like any rule, there are possible exceptions. But you're much better >>> off factoring your code better. >>> >>> I haven't managed to understand your software description, so i'm not >>> making a specific suggestion. But I know others have pointed out that >>> you should do as little as possible in top-level code of an imported >>> module. Make the work happen in a function, and call that function from >>> the original script, not from inside some import. An imported module's >>> top-level code should do nothing more complex than initialize module >>> constants. >>> >>> >>> -- >>> >>> DaveA >>> >>> > > (You top-posted, which makes it harder to figure out who said what.) > > For docs on the threading thing, see: > > http://docs.python.org/library/threading.html > > " ... an import should not have the side effect of spawning a new thread > and then waiting for that thread in any way..." > > > > > -- > > DaveA >
Thanks. I had read that as forbidding "waiting for that thread", not forbidding spawning a new thread. The following sentence says, "Failing to abide by this restriction can lead to a deadlock if the spawned thread directly or indirectly attempts to import a module." I gather that a clearer, more forceful statement might be, "Failing to abide by this restriction WILL lead to a deadlock if the spawned thread directly or indirectly attempts to import a module." All of which implies the behavior I've seen in various experiments, namely that as long as the spawned thread doesn't do any imports, I haven't seen any problems with spawning a thread in an imported module. I take your word for it that this is a no-no, but I don't know why. Bruce Sherwood -- http://mail.python.org/mailman/listinfo/python-list
