Personally: Python has a great type checker. Several, actually. They're not compile time, because Python doesn't exactly have a compile time, but still. 11/10,

Personally: Python has a great type checker. Several, actually. They're not compile time, because Python doesn't exactly have a compile time, but still. 11/10, use everywhere, spend less time on unit tests, be happy. Second, to me, these sorts of concerns about refactoring are. . . maybe not a smell, but worrisome, all the same. They suggest poorly-modularized designs with no internal component boundaries that might have limited the scope of impact of such a change. That said, even if you do find yourself needing to do a far-reaching refactor like that, refactoring in a dynamic codebase isn't necessarily harder, it's just different. Not being able to lean on the compiler to help you boil the ocean, for example, is fine, because boiling the ocean wasn't necessarily the best approach in the first place. The strangler pattern will help here, not just with type errors, but also with other problems the compiler might not have been able to help with, and will also be friendlier to the people who do your code reviews.