[Zope-dev] _getOb or __getattr__?
Hi, I need a product with custom attribute getting code and so looked to the BTreeFolder product for inspiration. It implements both __getattr__ and _getOb which appear to do roughly the same thing. What's the difference? Shane hints that __getattr__ is slower but allows acquisiton. Why is that? TIA, 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] _getOb or __getattr__?
On 2/27/01 10:59 AM, in article [EMAIL PROTECTED], "Chris Withers" <[EMAIL PROTECTED]> wrote: > Hi, > > I need a product with custom attribute getting code and so looked to the > BTreeFolder product for inspiration. > > It implements both __getattr__ and _getOb which appear to do roughly the same > thing. > > What's the difference? > > Shane hints that __getattr__ is slower but allows acquisiton. Why is that? _getOb and _setOb are for placing subobjects somewhere besides attributes (which is the default implementation). _getOb and friends are the default protocol that *SHOULD* be used by systems that change subobjects (ie - copy and paste). Jeffrey P Shell, [EMAIL PROTECTED] http://www.digicool.com/ | 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] _getOb or __getattr__?
Jeffrey P Shell wrote: > > _getOb and _setOb are for placing subobjects somewhere besides attributes > (which is the default implementation). When would __getattr__ be used then? 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] _getOb or __getattr__?
Jeffrey P Shell wrote: > > _getOb and _setOb are for placing subobjects somewhere besides attributes > (which is the default implementation). > > _getOb and friends are the default protocol that *SHOULD* be used by systems > that change subobjects (ie - copy and paste). Sorry, just thought of another coupla questions: If x is an instance of my class, then: If I do x.a = 1, is _setOb called? If I do print x.a, is _getOb called? 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] _getOb or __getattr__?
"Chris Withers" <[EMAIL PROTECTED]> wrote: > Jeffrey P Shell wrote: >> >> _getOb and _setOb are for placing subobjects somewhere besides attributes >> (which is the default implementation). > > When would __getattr__ be used then? > In what context? You could wire __getattr__ to call into _getOb (and probably __getitem__ too, since that's also used in traversal and as a way of getting non-Pythonic ID'd objects). def __getattr__(self, attr): return self._getOb(attr) Until very recently, __getattr__ on persistent objects was like playing with nuclear fire. But now, I *believe* it behaves properly, which means __getattr__ gets called when it receives an unknown name. How that affects Acquisition, I don't know. ___ 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] _getOb or __getattr__?
> Sorry, just thought of another coupla questions: > > If x is an instance of my class, then: > If I do x.a = 1, is _setOb called? > If I do print x.a, is _getOb called? No in either case. _setOb shouldn't be used directly in the current ObjectManger implementation. It doesn't populate the _objects list of the object manager on which it was called (your object won't show up). Instead, _setObject should be called. ___ 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] _getOb or __getattr__?
Chris McDonough wrote: > > > Sorry, just thought of another coupla questions: > > > > If x is an instance of my class, then: > > If I do x.a = 1, is _setOb called? > > If I do print x.a, is _getOb called? > > No in either case. > > _setOb shouldn't be used directly in the current ObjectManger > implementation. It doesn't populate the _objects list of the object manager > on which it was called (your object won't show up). Instead, _setObject > should be called. well, thankfully, I'm not going near __setattr__, _setOb or _setObject :-) On the setting side, only __setitem__ is getting meddled with, and I'm guessing there's not gotachas there? Anyway, using these methods: # attribute - based traversal stuff def _getOb(self, name, default=_marker): print '_getOb:',name try: return higher_getOb(self,name) except: import sys print 'type:',sys.exc_type print 'value:',sys.exc_value raise AttributeError,name def __getattr__(self,name,higher_getattr=higher_getattr): #print '__getattr__:',name try: return higher_getattr(self,name) except AttributeError: import sys #print 'type:',sys.exc_type #print 'value:',sys.exc_value raise AttributeError,name def __getitem__(self,name,higher_getitem=higher_getitem): print '__getitem__:',name try: return higher_getitem(self,name) except KeyError: import sys #print 'type:',sys.exc_type #print 'value:',sys.exc_value raise KeyError,name ...it would appear that unrestrictedTraverse first tries to use getattr and then tries to use getitem to get a name. That much I can veryify from the code ;-) However, it would appear that somewhere in a __getitem__ as implemented by ZCatalog, _getOb ends up getting called. Which is a little confusing :-S I think I know when the __get methods get called; same as normal python right? But when, why, how and what by does _getOb and/org _getObject and/or anything else I might be interested about in this space get called? ;-) Thanks loads for the help so far, 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] _getOb or __getattr__?
Chris Withers wrote: > > Hi, > > I need a product with custom attribute getting code and so looked to the > BTreeFolder product for inspiration. > > It implements both __getattr__ and _getOb which appear to do roughly the same > thing. > > What's the difference? _getOb() is part of the ObjectManager interface. If you want to store objects in your special ObjectManager in a special way, you override _getOb(), _setOb(), and _delOb(). (I didn't check the spelling--see ObjectManager.py) However, if you store objects in your ObjectManager in a different way than using setattr(self, name, value), acquisition won't find your subobjects because acquisition only looks at object attributes. It doesn't know anything about _getOb(). (And it's not a good idea to teach it to use _getOb(); think what it would be like if a Xeon ran like a 386...) Overriding __getattr__() lets you make acquisition work again. However, as Jeffrey said, until a few months ago it was forbidden. Then Jim fixed it. Now it's used extensively by BTreeFolders, Transparent Folders, and even the CMF. However, every time the acquisition machinery calls a __getattr__() you get a performance hit in the range of a few microseconds. But the products I listed try hard to minimize that impact, so it's not enough of an issue to warrant a C implementation. BTreeFolder.py provides a base class that doesn't have __getattr__(). You can use that if you think __getattr__() is slowing down your site. The derived class is what most people use because it provides the full functionality. Shane ___ 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] _getOb or __getattr__?
> subobjects because acquisition only looks at object attributes. It > doesn't know anything about _getOb(). (And it's not a good idea to > teach it to use _getOb(); think what it would be like if a Xeon ran like > a 386...) I remember the days when... ;-) Seriously though, why would that make it so slow? Is _getOb() often an expensive operation? thanks for all the info, 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] _getOb or __getattr__?
Chris Withers wrote: > > > subobjects because acquisition only looks at object attributes. It > > doesn't know anything about _getOb(). (And it's not a good idea to > > teach it to use _getOb(); think what it would be like if a Xeon ran like > > a 386...) > > I remember the days when... ;-) > > Seriously though, why would that make it so slow? Is _getOb() often an > expensive operation? No. The expensive part is invoking Python code from C. It's the same problem described by the documentation for the Python sort() method: it's much faster to sort() then reverse() than it is to sort() with a comparison function that reverses the elements. Invoking C from Python is fast, but invoking Python from C apparently requires a lot of work. Shane ___ 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] _getOb or __getattr__?
Shane Hathaway wrote: > > No. The expensive part is invoking Python code from C. It's the same > problem described by the documentation for the Python sort() method: > it's much faster to sort() then reverse() than it is to sort() with a > comparison function that reverses the elements. Invoking C from Python > is fast, but invoking Python from C apparently requires a lot of work. Thanks, that actually explains (completely unrelated to __getattr__ ;-) why one of our Zope products is so dog slow right now :-) 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] _getOb or __getattr__?
On Wed, 07 Mar 2001 09:49:09 -0500, Shane Hathaway <[EMAIL PROTECTED]> wrote: > Invoking C from Python >is fast, but invoking Python from C apparently requires a lot of work. Invoking a python function from anywhere (even from another python function) requires alot of work. Toby Dickenson [EMAIL PROTECTED] ___ 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 )
