Re: [Zope-dev] Re: ComputedAttribute
Martijn Pieters wrote: But because _v_* variables don't get pickled, another thread will never see them. If you want non-persisting (volatile) variables shared between threads, you'll have to devise your own mechanism for assuring the thread-safety of those variables. Or, instead of devising your own mechanism, you can borrow someone else's: http://www.handshake.de/~dieter/pyprojects/zope/SharedResource.html Thanks Dieter! -- Steve Alexander Software Engineer Cat-Box limited http://www.cat-box.net ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] Re: ComputedAttribute
Martijn Pieters wrote: Erm. The ExtensionClass.stx documentation hints at a ComputedAttribute class (but as an example of how you could use an ExtensionClass). The current C implementation of ComputedAttribute is not, as far as I can see, documented. Now I think I know the answer to this one, but I'll ask just to be sure: class MyClass(Persistent Acquisition.Explicit): def _set_your_attribute (self,value): self._v_your_attribute = value def _get_your_attribute (self): return self._v_your_attribute your_attribute = ComputedAttribute(_get_your_attribute) ...with this class, your_attribute isn't going to play in Persistence, is it? (so I can update it lots without worrying about ZODB size growing... :-) Hmm... more questions: If I do: x = MyClass() x.your_attribute = 1 ...what happens? Where do you import the ComputedAttribute module from? cheers, Chris ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] Re: ComputedAttribute
On Wed, Jan 10, 2001 at 04:13:49PM +, Chris Withers wrote: Martijn Pieters wrote: Erm. The ExtensionClass.stx documentation hints at a ComputedAttribute class (but as an example of how you could use an ExtensionClass). The current C implementation of ComputedAttribute is not, as far as I can see, documented. Now I think I know the answer to this one, but I'll ask just to be sure: class MyClass(Persistent Acquisition.Explicit): def _set_your_attribute (self,value): self._v_your_attribute = value def _get_your_attribute (self): return self._v_your_attribute your_attribute = ComputedAttribute(_get_your_attribute) ...with this class, your_attribute isn't going to play in Persistence, is it? (so I can update it lots without worrying about ZODB size growing... :-) Yup, this allows you to alias your_attribute to _v_your_attribute without creating an attribute that *will* persist in the process. Hmm... more questions: If I do: x = MyClass() x.your_attribute = 1 ...what happens? your_attribute is set to one instead of the ComputedAttribute instance and concequently persisted. If you want _set_your_attribute to be called, you need to override __setattr__: def __setattr__(self, name, value): setter = getattr(self, '_set_' + name, None) if setter: setter(value) else: raise AttributeError, "no such attribute: " + `name` Where do you import the ComputedAttribute module from? from ComputedAttribute import ComputedAttribute -- Martijn Pieters | Software Engineer mailto:[EMAIL PROTECTED] | Digital Creations http://www.digicool.com/ | Creators of Zope http://www.zope.org/ - ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] Re: ComputedAttribute
Martijn Pieters wrote: ...with this class, your_attribute isn't going to play in Persistence, is it? (so I can update it lots without worrying about ZODB size growing... :-) Yup, this allows you to alias your_attribute to _v_your_attribute without creating an attribute that *will* persist in the process. yay! :-) your_attribute is set to one instead of the ComputedAttribute instance and concequently persisted. d'Oh... of course... If you want _set_your_attribute to be called, you need to override __setattr__: def __setattr__(self, name, value): setter = getattr(self, '_set_' + name, None) if setter: setter(value) else: raise AttributeError, "no such attribute: " + `name` Hmmm... how would you change this to call the __setattr__ that was there before you overrode it, if a setter could not be found? cheers for all the help, this thread might make quite god docs for ComputedAttribute ;-) Chris ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] Re: ComputedAttribute
On Wed, Jan 10, 2001 at 05:07:07PM +, Chris Withers wrote: If you want _set_your_attribute to be called, you need to override __setattr__: def __setattr__(self, name, value): setter = getattr(self, '_set_' + name, None) if setter: setter(value) else: raise AttributeError, "no such attribute: " + `name` Hmmm... how would you change this to call the __setattr__ that was there before you overrode it, if a setter could not be found? The same way you call any overridden method, by calling it on the class you inherit it from. So: class Foo: def __setattr__(self, name, value): # Whatever pass class Bar(Foo): def __setattr__(self, name, value): Foo.__setattr__(self, name, value) # More whatever -- Martijn Pieters | Software Engineer mailto:[EMAIL PROTECTED] | Digital Creations http://www.digicool.com/ | Creators of Zope http://www.zope.org/ - ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] Re: ComputedAttribute
Chris Withers writes: Martijn Pieters wrote: Now I think I know the answer to this one, but I'll ask just to be sure: class MyClass(Persistent Acquisition.Explicit): def _set_your_attribute (self,value): self._v_your_attribute = value def _get_your_attribute (self): return self._v_your_attribute your_attribute = ComputedAttribute(_get_your_attribute) with this class, your_attribute isn't going to play in Persistence, is it? (so I can update it lots without worrying about ZODB size growing... :-) But, as I understand it, it is only updated in the thread that did the update. Your next request may get a different thread and see a different value. Dieter ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] Re: ComputedAttribute
Chris Withers writes: with this class, your_attribute isn't going to play in Persistence, is it? (so I can update it lots without worrying about ZODB size growing... :-) But, as I understand it, it is only updated in the thread that did the update. Your next request may get a different thread and see a different value. Huh? If I change self._v_your_attribute it's only going to get updated in one thread? That's a bit sucky :-S Doesn't matter in this _particular_ case 'cos this var gets set at the start of every request, but I'm a bit concerned about its general use... any help is good help :-) Chris ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] Re: ComputedAttribute
On Wed, Jan 10, 2001 at 11:09:43PM +0100, Dieter Maurer wrote: Chris Withers writes: Now I think I know the answer to this one, but I'll ask just to be sure: class MyClass(Persistent Acquisition.Explicit): def _set_your_attribute (self,value): self._v_your_attribute = value def _get_your_attribute (self): return self._v_your_attribute your_attribute = ComputedAttribute(_get_your_attribute) with this class, your_attribute isn't going to play in Persistence, is it? (so I can update it lots without worrying about ZODB size growing... :-) But, as I understand it, it is only updated in the thread that did the update. Your next request may get a different thread and see a different value. Indeed, only persistent variables are shared between threads (and globals of course, which creates a need for some kind of protection). -- Martijn Pieters | Software Engineer mailto:[EMAIL PROTECTED] | Digital Creations http://www.digicool.com/ | Creators of Zope http://www.zope.org/ - ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] Re: ComputedAttribute
On Wed, Jan 10, 2001 at 11:37:55PM -, Chris Withers wrote: Chris Withers writes: with this class, your_attribute isn't going to play in Persistence, is it? (so I can update it lots without worrying about ZODB size growing... :-) But, as I understand it, it is only updated in the thread that did the update. Your next request may get a different thread and see a different value. Huh? If I change self._v_your_attribute it's only going to get updated in one thread? That's a bit sucky :-S Doesn't matter in this _particular_ case 'cos this var gets set at the start of every request, but I'm a bit concerned about its general use... any help is good help :-) The whole threading spiel in Zope works because of ZODB persistence; any thread accessing an object whose variables have been changed has to retry with a fresh copy from the ODB. But because _v_* variables don't get pickled, another thread will never see them. If you want non-persisting (volatile) variables shared between threads, you'll have to devise your own mechanism for assuring the thread-safety of those variables. -- Martijn Pieters | Software Engineer mailto:[EMAIL PROTECTED] | Digital Creations http://www.digicool.com/ | Creators of Zope http://www.zope.org/ - ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
