Douwe van der Meij: AOP in Python API design

published May 11, 2012

Douwe van der Meij talks about Aspect Oriented Programming in Python API design at PyGrunn.

See the PyGrunn website for more info about this one-day Python conference in Groningen, The Netherlands.

Aspect oriented programming is more often used in Java than Python. I have used Java before, so I tried using this concept in Python now.

The use case was BioBench, which is one of the sponsors of this conference. It is an application for biogas installations. A farmer enters measurements and gets info from this.

One aspect you need for your API is security. Also statistics/logging, serialization. Probably more. The danger is that those aspects are scattered all over your code base and are tangled, interweaved with other aspects.

Aspect Oriented Programming means: separating your concerns. Put each aspect in a separate module. How can you implement this in pure python? Decorators!

What is an aspect:

  • pointcuts, a signature of your code, a regular expression (though I don't use it in my Python code)
  • join points: point in your code where the pointcut expression is true, so where the advices should be run
  • advices: code to run before or after the join point, or around it.

The security code is an 'around' advice. If a condition is true, we execute the main code, otherwise we skip it and raise an exception.

So for example you end up with:

def api_call(...):

It is good to apply this for aspects that are orthogonal to your main code, like (mostly) security.

Audience: in Zope you can use zcml for aspect oriented programming.