What Zope can learn from Zope

Filesystem development

Zope 2 has a user interface in which software development can take place. Limited, untrusted Python code is stored in the object database. This has two major drawbacks:

• it's Python, but Python with a few twists: untrusted so normal imports and operations are not always possible, and implicit acquisition pulling things in everywhere. This sucks, we want to use Python the way it is designed to be.

• you can't use normal file system tools to manage your code. Instead you have to use the web browser UI. That still isn't ideal even with modern AJAX goodness, and certainly wasn't ideal in 1999. It means reimplementing all the tools that already exists (editors, version control systems, searching, etc) on top of Zope. This was an attractive effort that many in the Zope community undertook, and most of that work is now lost.

Zope 2 development through the filesystem was also possible, but it has a completely different development model than the through the web development, and this accounts for part of the infamous Z-shaped learning curve of Zope 2.

Zope 3, and Grok, have filesystem-based development only. You just write normal Python code in normal Python modules which reside in normal Python packages. You use your favorite editor, and your favorite version control system.

Fine-grained components

Zope 2 introduced a powerful component programming model. Zope 2 is extensible through so-called Products, which often were used to create new ways to help developers program in the web UI. As an example, one product I wrote back in 2001 is called Formulator, which helps people construct web forms by putting together fields in the Zope UI.

Unfortunately Zope 2 components are rather coarse-grained. Single Zope 2 components would have to inherit from a lot of mixin classes in order to play within the Zope 2 framework, fattening up their APIs to unmanageable sizes. Components would be so coarse-grained it became hard to reuse them in other contexts, as they would make assumptions that were hard to override. It was hard to just use Formulator's widget classes and not its Form class for instance.

Zope 3 instead has a powerful component model that allows for fine-grained components. These components define interfaces which typically only provide a few methods, and this allows for loosely-coupled development and true reusable components. We distribute these components in many separate packages, which allows for a lot of flexibility - application developers may choose not to use some.

A user-interface

So the Zope 2 user interface has drawbacks for developers. It locks code into a hard to manage Zope-only format. It was also Zope 2's killer feature.

Zope 2's through the web user interface contributed enormously to Zope 2's success. Zope 2 was being adopted by non-Python programmers who discovered they could be very productive using the Zope 2 UI. These developers often turned into full-fledged Python programmers later on.

A user interface offers discoverability: in Zope 2 you get a drop-down list of components you could add to your object database. See an unfamiliar one? Just try creating one of those, see what UI options it presents, and click the "help" button. The UI encouraged experimentation and learning.

The Zope 2 UI also allows less hardcore developers to easily tweak layouts here and there and do a bit of simple scripting.

The Zope 2 UI was also used as a crude CMS and often extended to build simple CMSes that were still quite powerful for their time. In this sense the Zope 2 UI was quite similar to the admin UI that is one of the killer features of Django.

Zope 3 has lost almost all of this. Zope 3 does have a UI modeled after Zope 2's, but it's rarely used. Zope 3's UI was intentionally cripped compared to Zope 2's to prevent unmaintainable code to be created, and some ideas existed for checking out code from the object database for development on the filesystem, but it never really went anywhere. As a result Zope 3 is only approachable for Python developers, and is harder for beginners to pick up.

Grok has made Zope 3 a lot more approachable already, and I think is competitive with the other modern Python web frameworks, but a user interface could bring many more people in beyond this.

The Zope 2 UI had the drawback that it was all UIs in one, and did none of them very well as a result. I think we should work on bringing back most of the features of the Zope 2 UI back to Zope 3:

• an introspector UI. See what content objects are stored in your database, what APIs they offer, what views exist for them. There is a Zope 3 apidoc tool that does this. In addition, the Grok introspector was developed in last year's summer of code, and more work on it was done in this year's summer of code.

• a management UI: install, uninstall, configure and monitor applications and the server. Grok has a simple UI that allows you to do this. There is also the ZAM effort.

• a through the web development UI: we shouldn't be thinking about a full-fledged IDE here. This one should be tackled carefully, step by step. Tweaking page templates is something that could be presented in a UI quite well, for instance. Some work to this effect was done in the five.customerize package.

• an "editing backend" - it would offer navigation through the object tree, would display the contents of containers and would allow form-based editing of schema-driven contents. This would help provide a "good enough" solution for many applications that need some form of editing backend.

A component with a user interface starts to look like the coarse grained components of Zope 2. We should therefore be careful: the user interface should be easily replaceable and de-installable. We shouldn't be locked into it, but it should be there when we need it.

The good news is that many of the pieces are already in place for this work, and we should continue these efforts.