>> it helps when you do a refactoring that changes the type of the value passed somewhere from number to number[] Typing isn't a strong enough tool to combat t

>> it helps when you do a refactoring that changes the type of the value passed somewhere from number to number[] Typing isn't a strong enough tool to combat that class of problem; you can fix the type signatures while introducing a semantic break. You need tests and if you have tests, what does typing bring? Keep your tests fast, measure and maintain a speed of >250 tests per second and remember to test behaviour not implementation - you won't go far wrong. IDEs have been performing refactoring changes on our behalf in dynamic languages for years at this point. Don't manually edit when we've never had such powerful tooling available to us * https://www.jetbrains.com/help/pycharm/product-refactoring-tutorial.html * https://www.jetbrains.com/help/pycharm/structural-search-and-replace.html Even concepts that i'd say are strictly the domain of static typying, like automatically pruning dead code behind retired feature flags, make headway today: https://github.com/jendrikseipp/vulture https://github.com/jendrikseipp/vulture Typing has a time and a place, that is without a doubt but the world is better viewed without the static typing lens permanently affixed in place, your efficacy will increase.