David Wahler wrote: > Kent Johnson wrote: > > Is there a way to persist a class definition (not a class instance, > > the actual class) so it can be restored later? A naive approach > > using pickle doesn't work: > [snip] > > The idea is to persist classes that are created and modified at runtime. > > I couldn't resist the challenge, so I decided to take a crack at it. My > code is below. (I hope it's OK to post it even though it's a bit on the > long side.) So far, it seems to work OK; the biggest caveat to be aware > of is that functions' global context is not preserved. > > My approach was to use pickle's __reduce__ protocol to store functions > and classes. Of course, you can't modify the built-in function and > classobj types, so I subclassed Pickler to override them. The advantage > of this is that you don't need an extension to the pickling data > format, and you can use the standard unpickler. (The custom module > still needs to have been imported, as it adds the classobj type to > __builtins__.) > > Unfortunately, I'm not sure how to go about making it work for > new-style classes. It would seem to involve messing with dictproxy and > descriptor objects, and that's getting me into more unfamiliar > territory. > > I'm sure there's a better way to do this; this seemed like "the > simplest thing that could possibly work".
This is actually pretty sweet. It seems to me that you'll be fine with new-style classes if you just save dict(ob.__dict__) instead of trying to save __dict__ directly, as that'll get rid of the dictproxy part. There's no generic way to save descriptors, as far as I know, but you can always register reducers for specific types, like property, and user-defined descriptor classes are likely to be picklable anyway. As for functions' global context, you could look to see if there's a __name__ present, in which case you can save a reference to that module's __dict__. Otherwise, simply pickle the func_globals as-is. Some folks might just want to do that anyway, if the code isn't actually being loaded from a module. Of course, the classic caveat regarding pickles and security applies to all this. That is, pickles and security don't mix. If you want one, you can't really get the other. ;-) -- http://mail.python.org/mailman/listinfo/python-list
