[bslatkin]

I agree that another language that's better for functional programming would make this more compelling. Python has a lot of limitations in this area. I think all of those alternatives you listed (Julia, Clojure, etc) include turn-offs for Python programmers that are deal breakers. So I'm seeking another language that appeals to Python programmers but has more of the attributes that are amenable to functional programming.

[z9znz]

IMO, Ruby is a better general purpose "scripting" language like Python that has cleaner and more consistent features - including ones that lend themselves to functional approaches. Outside of web development it doesn't have the same appeal as Python due to the larger Python ecosystem... (many companies think they want to and will do "data science!")

Also, in my experience, Pythonistas tend to be more resistent to paradigm changes. So often I have heard, "Why would you want to do that?", or "This works fine as it is.". Not that I'm a fan of list comprehensions in Python (I think they're awkward and ugly compared to Ruby collection operations), but Python codebases I have had the displeasure of working in had lots of nested loops, mutations everywhere, copy-pasted code, and 30+ line methods. Trying to encourage single-responsibility, composability, less OOP, and more pure functions is like shoveling water uphill.

With both Ruby and Python you do need to be a bit thoughtful about unnecessary collection copies (which you would tend to favor when writing pure functions); but often you have a good sense of how large a volume of data you are handling and where copies will be particularly slow or heavy to do. When necessary, you can have an impure function that mutates input data, and at least in Ruby you can warn callers of the impending mutation by adding the ! to the function name. update_order!(order).