Yes, there most certainly is a type. It's dynamic, but not nonexistent. Now, of course you don't know the type for sure unless you run the code. I said so at the start. But I'm saying, can't you do a pretty good job in most cases? In this case, you could go to all places where do_something is called and see what objects are being passed in.

Yes, maybe there are situations where dozens of different types are passed in by different calls, or where we're building a library and we don't have any calls to do_something in our codebase, and cases where everything is obfuscated by one means or another. But depending on style I bet there are lots of cases where it works out ok.