[Zope] Using Interface module

[Terry Hancock]

I'm trying out the Interface module that comes with Zope
and is highly recommended by the ZDG and a number of
how-tos for product developers.

It seems, though, that there are some fuzzy areas specific
to Zope, and I'm wondering if anybody has some wisdom
on the "best practices" in these cases:

1) An interface contains several factory-function generated
methods -- ZSQL, DTML, or images.  

For example, I have a "pluggable brain" interface that 
wraps a product in a store -- the caller doesn't know 
exactly how the object should be displayed in a listing, 
because it doesn't know what kind of object it is.  So, the 
object provides DTML snippets to render itself in a 
selected range of  representational intents -- from full 
display to a brief catalog listing.  Obviously this code 
will break if the object does not provide the appropriate 
DTML method -- so we need to include it in the interface 
spec.

But what is it?  Technically it's a method, so maybe I 
should use the method interface definition approach:

def my_dtml_form(part_num=0, **kw):
    """Represents a part."""

But it looks more like an attribute when you define it -- 
do I lose anything by using one or the other representation?
(Obviously Attribute() doesn't give me the call signature --
anything else to consider?).

2) Sometimes, especially with factory methods, the methods 
and/or attributes needed are bound inside of __init__ (i.e. 
they're instance methods, not class methods).  Nevertheless,
they are a requirement for the interface. Should they be
listed in the interface?  Will the verification methods be 
able to figure this out when judging whether an instance 
will implement the interface?  Will valid classes fail 
because they don't list class attributes for these?

3) Finally, can I run some kind of self-verification step on
Zope import so that warnings or errors will result when a 
Product with broken implementations (i.e. objects don't
implement the interfaces they publish)? That seems like
it would be very useful for quality control purposes --
especially in an open-source project where many independent 
people of varying skill level might be modifying the code. 
It would make it a lot easier for developers if they could 
just get feedback on import.

Any thoughts appreciated. I'm really new to the interfaces 
concept, but I like the idea.

Cheers,
Terry

--
Terry Hancock ( hancock at anansispaceworks.com )
Anansi Spaceworks  http://www.anansispaceworks.com