Re: [Zope3-Users] Interface confusion (still)
On Tue, Jul 15, 2008 at 7:36 PM, Tim Cook <[EMAIL PROTECTED]> wrote: > And in my Maildir example it implements what is defined in IMaildir but > how does it 'provide' what is in IMaildirFactory? Specifically the > __call__ method. The __call__ of a class is the default constructor (the standard __new__/__init__ dance). Static and class methods of the class can also be used to support the interfaces of the class itself. > So my continuing thick-headed questions is: What does classProvides > really mean from a practical standpoint? Some kind of use case? Well, it sounds like you've already identified it as a way to describe the interface of the class (as a factory). It's not unusual for code using the component architecture to locate factories for objects by looking up a utility that provides the factory interface. That allows some nice ways to re-use composition-based constructs. -Fred -- Fred L. Drake, Jr. "Chaos is the score upon which reality is written." --Henry Miller ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
Re: [Zope3-Users] Interface confusion (still)
On Tue, Jul 15, 2008 at 7:27 PM, Fred Drake <[EMAIL PROTECTED]> wrote: > On Tue, Jul 15, 2008 at 6:56 PM, Benji York <[EMAIL PROTECTED]> wrote: >> When one says that a class *provides* an interface they're saying that >> instances of that class *implements* the interface. > > Sorry, you got that backwards. Instances provide the interfaces their > class implements. Darn, I always do that. ;) -- Benji York Senior Software Engineer Zope Corporation ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
Re: [Zope3-Users] Interface confusion (still)
On Tue, 2008-07-15 at 19:27 -0400, Fred Drake wrote: > On Tue, Jul 15, 2008 at 6:56 PM, Benji York <[EMAIL PROTECTED]> wrote: > > When one says that a class *provides* an interface they're saying that > > instances of that class *implements* the interface. > > Sorry, you got that backwards. Instances provide the interfaces their > class implements. Thanks. And in my Maildir example it implements what is defined in IMaildir but how does it 'provide' what is in IMaildirFactory? Specifically the __call__ method. So my continuing thick-headed questions is: What does classProvides really mean from a practical standpoint? Some kind of use case? --Tim -- ** Join the OSHIP project. It is the standards based, open source healthcare application platform in Python. Home page: https://launchpad.net/oship/ Wiki: http://www.openehr.org/wiki/display/dev/Python+developer%27s+page ** signature.asc Description: This is a digitally signed message part ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
Re: [Zope3-Users] Interface confusion (still)
On Tue, Jul 15, 2008 at 6:56 PM, Benji York <[EMAIL PROTECTED]> wrote: > When one says that a class *provides* an interface they're saying that > instances of that class *implements* the interface. Sorry, you got that backwards. Instances provide the interfaces their class implements. > On the other hand, lets say you had an IFooFactory interface that only > required that objects *providing* it be callable. In that case a class > Foo itself can *provide* the interface (because the class is callable). This is right. -Fred -- Fred L. Drake, Jr. "Chaos is the score upon which reality is written." --Henry Miller ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
Re: [Zope3-Users] Interface confusion (still)
On Tue, 2008-07-15 at 18:56 -0400, Benji York wrote: > On Tue, Jul 15, 2008 at 6:31 PM, Tim Cook <[EMAIL PROTECTED]> wrote: > > >> Note: classes *implement* interfaces, their instances *provide* them. > > > > ... and I am still confused about a use case for classProvides. > > When one says that a class *provides* an interface they're saying that > instances of that class *implements* the interface. > > On the other hand, lets say you had an IFooFactory interface that only > required that objects *providing* it be callable. In that case a class > Foo itself can *provide* the interface (because the class is callable). > > Make sense? Hmmm, not really. I tend to be VERY applied so how about an example from Zope? == class Maildir(object): """See `zope.sendmail.interfaces.IMaildir`""" classProvides(IMaildirFactory) implements(IMaildir) class IMaildirFactory(Interface): def __call__(dirname, create=False): """Opens a `Maildir` folder at a given filesystem path. ... class IMaildir(Interface): """Read/write access to `Maildir` folders. See http://www.qmail.org/man/man5/maildir.html for detailed format description. """ def __iter__(): """Returns an iterator over the pathnames of messages in this folder. """ def newMessage(): """Creates a new message in the `maildir`. = Now why wouldn't IMaildir just not inherit from IMaildirFactory instead of from Interface? If it did; what would be the effect of the difference(s) in approach to the rest of the application? Thanks, Tim -- ** Join the OSHIP project. It is the standards based, open source healthcare application platform in Python. Home page: https://launchpad.net/oship/ Wiki: http://www.openehr.org/wiki/display/dev/Python+developer%27s+page ** signature.asc Description: This is a digitally signed message part ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
Re: [Zope3-Users] Interface confusion (still)
On Tue, Jul 15, 2008 at 6:31 PM, Tim Cook <[EMAIL PROTECTED]> wrote: >> Note: classes *implement* interfaces, their instances *provide* them. > > ... and I am still confused about a use case for classProvides. When one says that a class *provides* an interface they're saying that instances of that class *implements* the interface. On the other hand, lets say you had an IFooFactory interface that only required that objects *providing* it be callable. In that case a class Foo itself can *provide* the interface (because the class is callable). Make sense? -- Benji York Senior Software Engineer Zope Corporation ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
Re: [Zope3-Users] Interface confusion (still)
The purpose of this question is related to an earlier question I had about using the best/correct schema field choice. It was pointed out that I should use 'Object' and set the schema to the interface of the class(es) that I wanted that attribute to accept. Since I did not point out that all of the classes that I wanted an attribute to accept would be descendants of that base class (and their interfaces) that is probably where I misunderstood that I would need to use classProvides. On Tue, 2008-07-15 at 21:39 +0200, Markus Kemmerling wrote: > An instance of a class provides not only the interface the class > declares to implement, but also all base interfaces of this > interface. In particular an instance that povides any interface, will > always provide 'Interface'. ... and that makes perfect sense. > Note: classes *implement* interfaces, their instances *provide* them. ... and I am still confused about a use case for classProvides. > You probably don't want to use 'classProvides' at all. The > 'implements(IDvText)' statement is enough for all instances of > 'DvText' to provide 'IDataValue'. Barring any replies to the contrary; I will remove all the superfluous classProvides calls. Since this makes sense to me and was my original understanding. Basically that interface inheritance acts just like class inheritance. Thanks, Tim -- ** Join the OSHIP project. It is the standards based, open source healthcare application platform in Python. Home page: https://launchpad.net/oship/ Wiki: http://www.openehr.org/wiki/display/dev/Python+developer%27s+page ** signature.asc Description: This is a digitally signed message part ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
Re: [Zope3-Users] Interface confusion (still)
Am 15.07.2008 um 20:53 schrieb Tim Cook: If interface B inherits from interface A and class B implements interface B; do I need to explicitly state that class B provides interface A? An instance of a class provides not only the interface the class declares to implement, but also all base interfaces of this interface. In particular an instance that povides any interface, will always provide 'Interface'. Concrete example: class IElement(Interface): value = Object( schema=IDataValue, title=_(u"value"), description=_(u"""Data value of this leaf."""), required=False ) class IDvText(IDataValue): ... class DvText(DataValue): implements(IDvText) classProvides(IDvText) The last line doesn't make any sense here. As I tried to explain before, if a class declares to 'implement' an interface, all of it's instances will provide it, whereby 'classProvides' declares the *class itself* to directly provide the interface. Note: classes *implement* interfaces, their instances *provide* them. Will Element.value allow instances of DvText or do I need to change the DvText classProvides call to: classProvides(IDataValue,IDvText) You probably don't want to use 'classProvides' at all. The 'implements(IDvText)' statement is enough for all instances of 'DvText' to provide 'IDataValue'. Regards, Markus Kemmerling ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
Re: [Zope3-Users] Interface confusion (still)
Hi, I believe not. In any case, implements, provides and such things are more like indications of what is being supported by a class and they are not enforced by runtime strictly. I just tried following: # from zope.component import * from zope.interface import * from zope.interface.verify import * class IA(Interface): pass class IB(IA): pass class B(object): implements(IB) verifyClass(IA, B) #returns True verifyClass(IB, B) #returns True verifyClass(Interface, B) #returns True class IC(Interface) : pass # Its usually a good idea to setup unit tests for testing these kind of things. With regards, - Shailesh On 7/15/08, Tim Cook <[EMAIL PROTECTED]> wrote: > > If interface B inherits from interface A and class B implements > interface B; do I need to explicitly state that class B provides > interface A? > > Concrete example: > > class IElement(Interface): > value = Object( >schema=IDataValue, >title=_(u"value"), >description=_(u"""Data value of this leaf."""), >required=False >) > > class IDvText(IDataValue): > > ... > > > class DvText(DataValue): > > > > implements(IDvText) > classProvides(IDvText) > > > Will Element.value allow instances of DvText or do I need to change the > DvText classProvides call to: > > classProvides(IDataValue,IDvText) > > Thanks, > Tim > > > > > > -- > Timothy Cook, MSc > Health Informatics Research & Development Services > LinkedIn Profile:http://www.linkedin.com/in/timothywaynecook > Skype ID == timothy.cook > ** > *You may get my Public GPG key from popular keyservers or * > *from this link http://timothywayne.cook.googlepages.com/home* > ** > > ___ > Zope3-users mailing list > Zope3-users@zope.org > http://mail.zope.org/mailman/listinfo/zope3-users > > > ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
[Zope3-Users] Interface confusion (still)
If interface B inherits from interface A and class B implements interface B; do I need to explicitly state that class B provides interface A? Concrete example: class IElement(Interface): value = Object( schema=IDataValue, title=_(u"value"), description=_(u"""Data value of this leaf."""), required=False ) class IDvText(IDataValue): ... class DvText(DataValue): implements(IDvText) classProvides(IDvText) Will Element.value allow instances of DvText or do I need to change the DvText classProvides call to: classProvides(IDataValue,IDvText) Thanks, Tim -- Timothy Cook, MSc Health Informatics Research & Development Services LinkedIn Profile:http://www.linkedin.com/in/timothywaynecook Skype ID == timothy.cook ** *You may get my Public GPG key from popular keyservers or * *from this link http://timothywayne.cook.googlepages.com/home* ** signature.asc Description: This is a digitally signed message part ___ Zope3-users mailing list Zope3-users@zope.org http://mail.zope.org/mailman/listinfo/zope3-users
