Thursday, January 29, 2015

Bottle vs. Flask vs. Django vs. a dozen others

There are times when a "micro framework" is actually useful. I wasn't easily convinced that this could be true. Big framework or die trying. Right?

Maybe not so right.

My primary example of a micro framework's value is a quick demo site to show how some API's are going to be consumed.

I've been avoiding an Angular.js app. We're going to be supporting the user experience with a sophisticated Angular.js app. But, as a back-end developer, I don't want to try to write demo pages in the proper app framework. There's too many ways to screw this up because I'll miss some key UX feature. Instead, I want to write fake pages that show a considerably simplified version of consuming an API. Sort of "suggestion" pages to clarify how the API's fit together.

To make it even more complex than necessary, I'm not interested in learning Angular.js, and I'm not interested in figuring out how it works. Running node.js, bower, npm, etc., etc., is too much.

[And Angular.js is just one version of the front-end. There's also mobile web, mobile native, tablet native, and God-alone-only-knows-what-all-else, to name a few. Each unique.]

Several sprints back, I slapped together two fake forms using bootstrap for layout and hosted them with Bottle. The navigation and framework look were simply copied from a screenshot and provided as static graphics. Lame, but acceptable. All that matters is getting the proper logo to show up.

The problem is that the sequence of API requests has grown since then. The demo grew to where we need a session so that alternative sequences will provide proper parameters to the APIs. We're beyond "Happy Path" interactions and into "what-if" demonstrations to show how to get (or avoid) a 404.

Bottle started with the significant advantage in fitting entirely into a single .py module. The barrier to entry was very low. But then the forms got awkwardly complex and Jinja2 was required. Now that sessions are required, the single module benefit isn't as enticing as it once was.

I've been forced to upgrade from Bottle to Flask. This exercise points out that I should have started with Flask in the first place. Few things are small enough for Bottle. In some ways, the two are vaguely similar. The @route() annotation being the biggest similarity. In other ways, of course, the two are wildly different. There's only a single Flask, but we can easily combine multiple Bottles into a larger, more comprehensive site. I like the composability of Bottles, and wish Flask had this.

The Flask Blueprints might be a good stand-in for composing multiple Bottles. Currently, though, each functional cluster of API's has their own unique feature set. The bigger issue is updating the configuration to track the API's through the testing and QA servers as they march toward completion. Since they don't move in lock-step, the configuration is complex and dynamic.

The transparent access to session information is a wonderful thing. I built a quick-and-dirty session management in Bottle. It used shelve and a "simple" cookie. But it rapidly devolved to a lot of code to check for the cookie and persist the cookie. Each superficially simple Bottle @route() needed a bunch of additional functionality.

The whole point was to quickly show how the API's fit together. Not reinvent Yet Another Web Framework Based On Jinja2 and Werkzeug.

Django seems like too much for this job. We don't have a model; and that's the exact point. Lacking a database model doesn't completely break Django, but it makes a large number of Django features moot. We just have some forms that get filled in for different kinds of events and transactions and searches and stuff. And we need a simple way to manage stateful sessions.

Omitted from consideration are the other dozen-or-so frameworks listed here: This is a great resource for comparing and contrasting the various choices. Indeed, this was how I found Bottle to begin with.