If you value time spent writing code higher than preventing bugs, I have doubts about the size of codebases you were maintaining. The reality I have experience

If you value time spent writing code higher than preventing bugs, I have doubts about the size of codebases you were maintaining. The reality I have experienced is that working with a large codebase in Python (talking 100kloc+ here, and teams larger than 3) is an absolute nightmare. Lack of explicit typing on argument values and returns means that everytime you add an argument to a function, or move things around, you are frantically grepping trying to find all the callers and hoping that you caught all of them. Add in the more functional aspects such as passing functions around and lambdas and *args and kwargs and different return types depending on function behavior and it gets very ugly. Given the fact that adding functionality and refactoring are the most common activities when working with a large existing codebase, this becomes very old, very quickly. I suspect that Guido's newfound interest in explicit typing coincides with his employment at Dropbox and Google and realizing the very real pain that comes with maintaining large Python codebases.