As someone who is not a web developer, but has a need to create a few internal apps, portable sounds like simple - exactly what I need.
My desire: (1) grab data, (2) render chart / graph, (3) display in browser
Without needs like session management, concurrency, etc., Bottle "sounds" easier, which is mostly based on the 1 file import thing, and why I was looking at Bottle last time I did not get this project rolling.
You can do the "1 file thing" with either. It's enforced in Bottle but not in Flask. I've used both and would recommend going with a Flask(web-framework)/SQLAlchemy(database or part that "grabs data") combo that sends JSON to a javascript chart/graph library.
You should be able to find a number of Flask/Backbone demos on github. Checking out a few of those would be a good place to start, even though you'll probably be scrapping backbone and just using a javascript charting library instead.
Based on your description here, you would do well to use either one. Just based of my experience, I'd go with Bottle, and when/if you hit the limit of its functionality, you can pretty much seamlessly convert between the two.
Flask is great, and offers you so much more flexibility, but there's just something about the simplicity of Bottle that draws me back to it whenever I need to make a simple web app.
I had looked at Bottle for a similar reason some time ago. Looking into using Bottle and Highcharts for a first experiment. Maybe Google Charts as well.
My desire: (1) grab data, (2) render chart / graph, (3) display in browser
Without needs like session management, concurrency, etc., Bottle "sounds" easier, which is mostly based on the 1 file import thing, and why I was looking at Bottle last time I did not get this project rolling.