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The entire language was built from the ground up using OOP concepts. IMHO that makes it more oop than just about anything else. Every aspect of the language can be manipulated including the object "Class" which can be manipulated on the fly as it's created.
It makes the language very easy to learn because so much of the language is polymorphic. Got a file handle, try the put method. Got a standard out handle, try the put method. Got a network socket, try the put method. . . . you get the idea. Working with ruby I feel like I need less of a reference than other languages. Once I get used to a particular class hierarchy I understand that most of the inherited methods are available for all classes in that tree.
I had a python stint and really liked the language, but feel that Ruby code is more expressive. I know that is cosmetic or semmantic which you seem to be trying to avoid. I think if I were defending python I would avoid them as well. :) In all seriousness tho, python is great . . . ruby is great. It's all about enjoying what you do and if python makes you happier than ruby then that's what you should do.