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

[Lennart Regebro]

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.

>  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.

> 2. Is it according to Zope-, Python-, ... philosophy ok to danymically implement
>    interfaces depending on the inner state of an object?

Uhm. IMO, no, not unless you really, really have to.

-- 
Lennart Regebro, Nuxeo     http://www.nuxeo.com/
CPS Content Management     http://www.cps-project.org/