This is a Flask App. It currently runs on Debug mode. To run enter the following command:
$ export FLASK_DEBUG=1
$ FLASK_APP=server.py flask run
/transactions operates at O(1) /statistics operates at O(N)
Initially I had a plan to run count() as a background task to "clean up" RET_TRANSACTIONS as the seconds of the app passed. Unfortunately, I had trouble making it work with the ThreadPoolExecutor.