Because there is no type. It's dynamic. You can't figure out what the type is unless you run the code.
def do_something(thing_a, thing_b):
...
What's the type of thing_a or thing_b?
There is none. There isn't even a type globally. thing_a and thing_b acquire new types at every call instance. This basically screws you for all useful auto-complete information.
You can't even do proper go-to-definition because of things like getattr.
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.
def do_something(thing_a, thing_b): ...
What's the type of thing_a or thing_b?
There is none. There isn't even a type globally. thing_a and thing_b acquire new types at every call instance. This basically screws you for all useful auto-complete information.
You can't even do proper go-to-definition because of things like getattr.