[Zope3-dev] Package organization quandry

[Jim Fulton]

Guido van Rossum wrote:
> 
> > There's a tradeoff between moving things out of App to encourage
> > their use outside of the Zope application server and keeping the
> > dependencies between things outside of App to a minimum.
> 
> One possible strategy is to avoid hard-coded dependencies and instead
> pass the necessary objects or classes in at construction time.  I
> think TAL already uses this approach: there's a default execution
> engine that's pretty simple and uses nothing except core Python; to
> get the ZPT engine you instantiate and pass it explicitly.  Maybe this
> idea can be extended?

This apporach doesn't work that well if there are a lot of clients of
the constructor. For example, users of PageTemplateFiles should be able
to:

   index = PageTemplateFile('index.zpt')

If people effectively always have to:

   index = PageTemplateFile('index.zpt', engine=ZopeEngine)

Then I think the extra argument is just a dead chicken 
(meaningless sacrifice;).  I'd as soon provide a constructor that
automated this. I could put this constructor in a separate package
in App. This is basically the option I'm considering.

The specialization involves more than just engine selection though.
For example, I have a class that specialized page templates to be
view methods, requiring changes in a number of methods and adding a 
__get__.

Jim

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