i was unfortunately responsible for this one…

we developed a wireless communication protocol which was specified in an excel sheet, and it fell on us devs to implement the message types specified in the sheet. however since the specification kept changing we had to constantly update the message types in our tests to make sure they conformed. so i said “fuck it” and built a program that allowed me to “import” an excel file in a python program, which exposed all messages as classes that could be instantiated with automatic unit conversions. just drop the excel file of the day in the right place and run the test suite.

anyway that’s how the excel sheet became the formal API definition