[Zope3-Users] Cloning interfaces/interface fields - how?

Marius Gedminas mgedmin at b4net.lt
Tue Feb 19 14:13:59 EST 2008

On Tue, Feb 19, 2008 at 04:46:29PM +0100, Hermann Himmelbauer wrote:
> I'm over and over confronted with a simple pattern, where I need to clone 
> interface field. For instance, I have the content object, which has an 
> interface, e.g.:
> class IPerson(Interface):
>   name = TextLine()
>   address = TextLine()
> Then, I have for instance a search form, which consists of fields of other 
> interfaces, therefore I tried this:
> class IPersonSearch(Interface):
>   name = IPerson['name']
> The above interface has the problem that the field is referenced, thus 
> changing attributes (e.g. name.required=False) changes also the attributes of 
> the original field.

Don't do that then.

> Therefore I now copy the field, which seems to work (but I'm not 100% 
> certain):
> class IPersonSearch(Interface):
>   name = copy.deepcopy(IPerson['name'])

I would not recommend this.

> Another idea is to entirley skip the IPersonSearch interface and create the 
> interface "on the fly", like this:
> class SearchFrom(z3c.form.EditForm):
>    fields = z3c.form.field.Fields(copy.deepcopy(IPerson).select('name'))

Strike out the deepcopy and you've got the correct solution:

  class SearchFrom(z3c.form.EditForm):
     fields = z3c.form.field.Fields(IPerson).select('name')

> However, this does not seem to work as still some things are referenced 
> instead of copied, so copy.deepcopy seems to fail on interfaces.

What are you trying to achieve?

Zope 3 schema fields ought to be treated as immutable objects.

> What's your opinion on this, how do you apply this pattern?

We don't modify fields, ever.  We use the power of zope.formlib (or
z3c.form) to get dynamic forms.

Marius Gedminas
NT 5.0 is the last nail in the Unix coffin. Interestingly, Unix isn't in the
coffin... It's wondering what the heck is sealing itself into a wooden box 6
feet underground...
                -- Jason McMullan
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