[Zope] Class variables in ZClasses

[Jim Fulton]

Darran Edmundson wrote:
> 
(snip)
> I'm confused about how class variables are implemented in
> Zope. 

I prefer to call these shared instance attributes.


> For example, let's say I have a ZClass with instance
> variable "Subject" which is a list of keys into a dictionary
> "SubjectChoices".  Rather than every instance maintaining a
> separate copy, SubjectChoices should be a class variable -
> all instances see the same dictionary.  Any insights would
> be most appreciated.

You simply have to arrange to get SubjectChoices to be an 
attribute of the class managed by the ZClasses.  If there
was a way to create dictionary properties, you could do this
via a propertysheet, since ZClass propertysheets create
default property values in classes.  Since Zope doesn't
give you a way to spell this through the web, you have to resort
to Python.  You could define a Python mix-in class that has
the property:

  class MixIn:

     SubjectChoices={...}

and mix it into your ZClass.

Alternatively, you could, from Python (either using the
Python interactive interpreter or an external method do
something like:

  import Zope
  app=Zope.app()
  app.Control_Panel.yourProduct.yourZClass.setClassAttr(
     'SubjectChoices',{...})
  get_transaction().commit()
  app._p_jar.close()

Jim


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