[python-uk] hexagonal Django

Jonathan Hartley tartley at tartley.com
Fri Aug 15 18:01:07 CEST 2014

I think what you describe is a common situation. When I reorganised that 
application in a Django project, that was one aspect that bugged some of 
my coworkers.

But I think there is potentially still some value there. The resulting 
one line business functions create a well-defined seam between your 
app's (slender) business logic and each of your interfaces to  external 
systems. That way, you make it easy for developers to avoid accidentally 
mixing 'django' code into the same module as code which talks to 

If you already have the discipline to maintain great separation of 
concerns (along these or other lines), which I'm guessing PythonAnywhere 
still does, then perhaps you don't need this particular constraint to 
help you maintain it.

Is there also value in helping you plug in fake external services for 
testing purposes? I believe there is, but again, I'm not sure this value 
is greater than zero if you *already* have well thought-out mechanisms 
for plugging in fake external systems.


On 15/08/14 11:22, Harry Percival wrote:
> Thanks Peter!  I was speaking to Brandon at Pycon this year and he was
> telling me this was going to be his next talk to take on the road, and I
> was definitely looking forward to seeing it.  Matt O'Donnell was also
> there, and he's done a talk on this sort of thing recently too (
> https://www.youtube.com/watch?v=NGhL7IA6Dik). It's definitely in the air.
> My own modest attempts to approach the subject are in my book -- in chapter
> 19, where I show how striving for test isolation can (theoretically) push
> you towards something like a lean architecture (
> http://chimera.labs.oreilly.com/books/1234000000754/ch19.html) and in
> chapter 21, the wrap-up, where I waffle on about all these things (
> http://chimera.labs.oreilly.com/books/1234000000754/ch22.html)
> I don't think I managed to broach the subject nearly as cleanly as Brandon
> did.  I really admire his talks.  His data structures talk was one of the
> top 3 I saw at Pycon this year (
> http://pyvideo.org/video/2571/all-your-ducks-in-a-row-data-structures-in-the-s).
> Perfect pace, slides that complement rather than repeat the talk,
> fascinating and useful content...
> Anyways, back to our onions - I guess the thing that's always bothered me a
> bit about the "clean architecture" is that my main project (pythonanywhere)
> is "all boundaries", to use Gary Bernhardt's terminology.  Or, to put it
> differently, I don't think we really have much in the way of "business
> logic".  We just turn Http requests into commands that go to processes.
> There's really not much in the way of "logic" in the way.  No calculations
> or business rules to speak of.  So it's never seemed worth it, to us.
> And sometimes I think -- aren't many web projects just thin CRUD wrappers
> around a database?  Is going to all the trouble of isolating your business
> logic from, eg, django, really worth it in most cases?
> On 13 August 2014 13:09, Daniel Pope <lord.mauve at gmail.com> wrote:
>> Coincidentally, I blogged on the topic of Django project organisation at
>> the weekend.
>> http://mauveweb.co.uk/posts/2014/08/organising-django-projects.html
>> May be of interest?
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Jonathan Hartley    tartley at tartley.com    http://tartley.com
Made of meat.       +44 7737 062 225       twitter/skype: tartley

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