Duck typing is great. Knowing that as long as my object does what the function expects it to, I can pass it to the function and get my results without having to worry about exactly what else my object might do. Coming from statically-typed languages such as Java and C++, this is incredibly liberating, and makes it easy to rapidly prototype complex and expressive code without worrying about checking types everywhere. This expressiveness, however, comes with a cost: type errors are only caught at runtime, and can be hard to debug if the original author didn’t document what that one variable in that one function signature is expected to look like.