A decently featured microblogging web application written in Python and Flask that I studied as part of Flask Mega-Tutorial. The code was in sync with current versions of Python and Flask in June 2016.
The tutorial referenced above explains how to setup a virtual environment with all the required modules.
The sqlite database must also be created before the application can run, and the db_create.py script takes care of that. See the Database tutorial for the details.
To run the application in the development web server just execute run.py with the Python interpreter from the flask virtual environment.