On 2 Abr, 21:38, "Chris Mellon" <[EMAIL PROTECTED]> wrote: > On Wed, Apr 2, 2008 at 2:33 PM, João Neves <[EMAIL PROTECTED]> wrote: > > On Apr 2, 5:41 pm, "Dan Upton" <[EMAIL PROTECTED]> wrote: > > > > The thing I've been wondering is why _is_ it read-only? In what > > > > circumstances having write access to co_code would break the language > > > > or do some other nasty stuff? > > > > > João Neves > > > > I can't speak to Python's implementation in particular, but > > > self-modifying code in general is unpleasant. It certainly is > > > possible to support it in runtime environments, but it's usually not > > > easy to do so. That is, of course, somewhat dependent on the > > > implementation of the runtime environment, and even to some degree the > > > underlying hardware. (For instance, the compiled code you want to run > > > could be in the hardware cache; if you then change the instructions at > > > those addresses in memory, it's not always straightforward to get the > > > processor to realize it needs to load the new data into the > > > instruction cache.) Plus, I suppose it might be possible to break > > > strong (even dynamic) typing if you start changing the code around > > > (although I can't construct an example off the top of my head). > > > Indeed, the caching issue is a relevant one I guess, and adding the > > mechanism to go around that might have a significant impact on > > performance. > > I haven't looked in detail into it, but I agree with your opinion > > concerning strong and dynamic typing. If type check is done while > > compiling to bytecode, there is no guarantee the modified bytecode > > will respect the rules, for instance. I don't know though, haven't > > really checked how it's done at this point. :) > > I will be fiddling around with the Python VM these days anyway, and > > since I'm going to muck around the bytecode, I might just try to see > > the effects of removing the read-only restriction from co_code. > > There is no need to overwrite co_code. Create a new code object with > your desired bytecode and use that instead.
Yes, it may work (haven't tested - isn't there any problem with stuff like co_name, for instance?), but for simplicity's sake, wouldn't it be far more convenient if you could just write over co_code? :) In the end, it's all a matter of convenience, I guess. -- http://mail.python.org/mailman/listinfo/python-list
