Why Python forbids multiple instances of one module?
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From: Ian Kelly on 5 Jul 2010 01:42 2010/7/4 CHEN Guang <dr.cg(a)126.com>: > Why Python forbids multiple instances of one module? > If only Python allows multiple instances of one module, module will > be enough to replace class in most cases. > After all, it is much easier to write a module than a class, at least we do > not have to write self everywhere. If you really want to do that, it should be possible by deleting the entry from sys.modules and re-importing it. You save yourself having to explicitly write self everywhere, but instead you have to declare all your "instance" variables as globals in each "method" that uses them, which isn't much less of a chore. You also lose inheritance, properties (and descriptors in general), magic method support, metaclasses, and pretty much all the other nice features that new-style classes have to offer.
From: Chris Rebert on 5 Jul 2010 01:49 2010/7/4 CHEN Guang <dr.cg(a)126.com>: > Why Python forbids multiple instances of one module? That's just how its import mechanism works. It allows for modules that need canonical program-wide state to rely on being singleton, and it's also an optimization. You can trick the import machinery and get around the restriction though. > If only Python allows multiple instances of one module, module will > be enough to replace class in most cases. Why do classes need replacement in the first place? Modules and classes serve distinct purposes. Also: How would you specify a class-module's superclasses? And what if a class depends on other modules/classes/packages? Then the class-module's namespace would be polluted with all the stuff it imported; ick. > After all, it is much easier to write a module than a class, at least we do > not have to write self everywhere. That seems a relatively petty reason; see also Ian's excellent point about `global`. Cheers, Chris -- Yay, Fireworks! http://blog.rebertia.com
From: kedra marbun on 6 Jul 2010 02:26
module obj is instance of types.ModuleType, which is instance of 'type', where class obj is instance of 'type'. even only at this point, they're diff in to many ways. there are so many things to do when you truly want module to replace class, as pointed by 2 posts above i'm also a beginner, so i can offer you a tip in learning it: follow the design, py usually has good reasons about it, i've lost in every challenge i put against py design, luckily i find the reasons through my own experiment. yes, it's better to find it through hacking, rather than people talking about it, the reason is the same as coding to learn programming, not only reading book. it will become more understandable when people say py has clean design as for 'self', yes i admit it seems troublesome at first, you'll have reason for it once you know that method is simply a func, you'll embrace the more general design (py requires you to specify a name for the caller) when you learn about metaclass. a nice argument to this is that human beings are visual creatures, it becomes so much easier to have a name that desribes the obj it points to (like 'self', 'cls', 'metacls') than implicit name that trying to be as general as possible (like 'this') |