[Zope3-Users] Re: How to manually define an object's provided interfaces?

[j.kartnaller]

Have a look at zope.interface.__init__.py -> alsoProvides

Jürgen

Frank Burkhardt wrote:
> Hi,
> 
> On Mon, May 29, 2006 at 01:31:03PM +0200, Lennart Regebro wrote:
>> On 5/29/06, Frank Burkhardt <fbo2 at gmx.net> wrote:
>>> I'm going to write an alternative implementation of
>>> zope.app.file.interfaces.IFile . This implementation will automatically
>>> determine the mime type of the data it's containing.
>>>
>>> I would like to add a method that determines (guesses), if the current file
>>> object contains an image...
>>>
>>> isimage=(mimetype(self.data).split('/')[0] == 'image')
>>>
>>> ... and I want to dynamically make the object implement another interface ...
>> Ehhh. Really? I must say that I find that a very suspiscious way of
>> handling that problem. Rather I would use a factory that generates the
>> correct type of object (image or file) from the data.
> 
> Different factories won't help because the user should be able to update
> the file object's content after ist was created.
> 
>>> if isimage:
>>>    IImage.provide(self)
>>> else:
>>>    IImage.dontprovide(self)
>>>
>>> Unfortunately, there is no 'provide' method on interfaces :-( .
>> Of course, you don't want to make an interface dynamically be another
>> interface, that just doens't make any sense. You could probably do it
>> by making the OBJECT provide different interfaces dynamically.
> 
> OK - this was a bit confusing. One more try:
> 
>  I want to make an object provided one interface (IFile) always and one
>  interface (IImage) "sometimes". Sometimes means "whenever libmagic thinks,
>  the file is an Image". I don't want to modify any interface but only the
>  object's list of provided interfaces.
> 
> Regards,
> 
> Frank