Pygrunn keynote: Morepath under the hood - Martijn Faassen¶

Tags: python, pygrunn, zope, django

(One of my summaries of the one-day 2016 PyGrunn conference).

Martijn Faassen is well-known from lxml, zope, grok. Europython, Zope foundation. And he’s written Morepath, a python web framework.

Three subjects in this talk:

• Morepath implementation details.

• History of concepts in web frameworks

• Creativity in software development.

Morepath implementation details. A framework with super powers (“it was the last to escape from the exploding planet Zope”)

Traversal. In the 1990’s you’d have filesystem traversal. example.com/addresses/faassen would map to a file /webroot/addresses/faassen.

In zope2 (1998) you had “traversal through an object tree. So root['addresses']['faassen'] in python. The advantage is that it is all python. The drawback is that every object needs to know how to render itself for the web. It is an example of creativity: how do we map filesystem traversal to objects?.

In zope3 (2001) the goal was the zope2 object traversal, but with objects that don’t need to know how to handle the web. A way of working called “component architecture” was invented to add traversal-capabilities to existing objects. It works, but as a developer you need to quite some configuration and registration. Creativity: “separation of concerns” and “lookups in a registry”

Pyramid sits somewhere in between. And has some creativity on its own.

Another option is routing. You map a url explicitly to a function. A @route('/addresses/{name}') decorator to a function (or a django urls.py). The creativity is that is simple.

Both traversal and routing have their advantages. So Morepath has both of them. Simple routing to get to the content object and then traversal from there to the view.

The creativity here is “dialectic”. You have a “thesis” and an “antithesis” and end up with a “synthesis”. So a creative mix between two ideas that seem to be opposites.

Apart from traversal/routing, there’s also the registry. Zope’s registry (component architecture) is very complicated. He’s now got a replacement called “Reg” (http://reg.readthedocs.io/).

He ended up with this after creatively experimenting with it. Just experimenting, nothing serious. Rewriting everything from scratch.

(It turned out there already was something that worked a bit the same in the python standard library: @functools.singledispatch.)

He later extended it from single dispatch to multiple dispatch. The creativity here was the freedom to completely change the implementation as he was the only user of the library at that moment. Don’t be afraid to break stuff. Everything has been invented before (so research). Also creative: it is just a function.

A recent spin-off: “dectate”. (http://dectate.readthedocs.io/). A decorator-based configuration system for frameworks :-) Including subclassing to override configuration.

Some creativity here: it is all just subclassing. And split something off into a library for focus, testing and documentation. Split something off to gain these advantages.