[fjh]

While I appreciate the sentiment of settling debates with data, you have to actually measure the right things. That statistic that says that only 2% of bugs would be prevented by static types? That's based on the assumption that everything that would be a type error in a statically typed language manifests as an exception in Python. But that's obviously not even close to being true. The really annoying bugs that type systems prevent are far more insidious than that. For example Python will happily let you use the greater-than operator on an int and a function. So if you accidentally write `f < 10` instead of `f() < 10`, you will not get a type error, but your program will have a bug that manifests in your program logic going wrong and leading to wrong results somewhere down the line.

I've analysed all bug tickets for a Python system at a previous job for several months, tracking how many of our bugs would have been prevented by a Haskell-style type system. This isn't very scientific either, but for my sample it was somewhere between 70%-90% depending on your interpretation. I'm not saying this generalises to all projects, but I can definitely say that the 2%-number is hilariously wrong.