A great practice in software development is clear error message communication.

Something like "An error occurred. Please try again later.", simply will not do because it’s simply easier to be explicit.

Our goal here would be to ensure that a consistent interface is communicated to our client applications regardless of request.

Tools and frameworks like Ruby-on-Rails make this really easy with it’s ActiveRecord implementation (Active record is literally a design pattern btw).

You’ll find that in most “fully featured” frameworks with ORMs like Rails, Django, Sails, etc, there is some sort of implementation that enables a clean interface for transmitting error messages, but often we don’t want to carry the bloat of these frameworks along.

Enter: types.

Most internet services are also financial services. From recurring subscription payments, investment banking, issuing transfers and payouts to bank accounts, consumer retail, forex exchanges, bitcoin, payroll services; take your pick, there is plenty of opportunity to work with finance in tech.

Building these services properly and securely should not be a challenge. No one should end up with something like $100.000000000000000034 showing up on their bank statement.

In this post, I’m going to show you how to build a minimal financial service with the use of python, Babel.numbers, FastAPI, and Rates API.