The Weirdness of Zope

Web UI

Zope featured a web-based user interface, which was rare thing at the time. The user interface was a hybrid between a CMS and a development environment. Using the web interface, people were able to construct and configure applications using HTML templates, scripts and SQL statements.

The Zope UI was an interesting experiment. It dramatically lowered the entry barrier for web development. It attracted a lot of people to Zope. This helped the Zope community grow, but also led to problems, as the next barrier to real Python web development was way too high.

In the end neither the CMS nor the development environment were sufficient. The Zope community moved on to build its own CMSes. I helped create one called Silva, but the really big one is Plone. Both are still around. Plone has always had a very vibrant community, something I witnessed again first hand last year at the Plone conference.

Extensibility

Although the APIs were sometimes weird, you could extend Zope with new components written in Python; just modules in files. Over time the Zope community -- at least the developers who could -- slowly moved away from the web user interface to write more and more code the Python way as Zope extensions. Writing code through a web user interface was too cumbersome -- it had a deliberately crippled Python for security reasons, and the code you wrote that way was hard to maintain too; integration with a version control system was difficult, for instance.

A rich ecosystem of new Zope components written in Python emerged from the Zope community. One of the first pieces of open source software that I wrote was a form component called Formulator that you could use to construct web forms using the Zope web user interface. People still use Formulator to this day.

Extensibility remained a focus of the Zope project throughout its history. In a future post I'll talk about some of the extensibility mechanisms that were introduced later.

ZODB

Another innovation of Zope was the Zope Object Database (ZODB). The ZODB is a Python object database, offering near transparent persistence for Python objects. Over time it grew clustering support and multiple storage backends. It is nearly magic: you write your Python class and derive from the Persistent base class, and as long as you attach instances of that class to a persistent root, they will continue to exist in the database automatically.

The ZODB was actually sometimes problem commercially -- try to explain to a customer that they should trust their data not to their precious SQL database but to this weird Python database. Imaging doing this years before the NoSQL movement emerged -- if you said "database" at the time, people thought relational database with SQL. NoSQL has certainly made it a lot easier now.

The ZODB is still around, and is very useful, though it does have some drawbacks. Its strength, the integration with the Python language, is also a source of some of its weaknesses. The ZODB is almost too intimate with the Python language, making it harder to use data in it outside of Python.

The intimacy between database and Python classes also makes it more cumbersome to change the structure of Python code -- changing a Python class can easily break its existing instances in the database if you aren't careful.

The ZODB also doesn't support a built-in query engine, though it does offer the tools to build one. I was one of the people who did (hurry.query), but a query engine is really one of those things you want to be taken care of by dedicated maintainers.

Acquisition

Zope also innovated on something that is too weird to go into much detail about here: acquisition. Store an object in an attribute of another, and it will gain all the attributes and method of its container. While sometimes useful it was a language innovation that went too far, and had too many unforeseen interactions. I see acquisition as an educational but failed experiment. If you want to read the documentation, or if you have a strange desire to shoot yourself in the foot, Acquisition is still available as a library on PyPI today.

This blog entry is a part of a series on Zope and my involvement with it. Previous. Next.