As for significant whitespace, the problem is that I'm often dealing with files with several thousand lines of code and heavily nested functions. It's very easy to lose track of scope in that situation. Am I in the inner loop, or this outer loop? Scrolling up and down, up and down to figure out where I am. Feels easier to make mistakes as well.
It works well if everything fits on one screen, it gets harder otherwise, at least for me.
As for types, I'm not claiming it's unique to Python. Just that it makes working with Python harder for me. Being able to see the type of data at a glance tells me a LOT about what the code is doing and how it's doing it - and Python doesn't let me see this information.
As for debugging, it's great if you have pure Python. Mix other languages in and suddenly it becomes pain. There's no way to step from another language into Python (or vice-versa), at least not cleanly and consistently. This isn't always true for compiled->compiled. I can step from C++ into Fortran just fine.