Just `pip install hy` and then `python -mhy` to run it. Once you see how Python translates into Hy, it's pretty straightforward.

    (import os)
    (import [os.path :as op])
    (with [f (open (op.join dir_name file_name) "w")]
        (.write f "..."))

Some things you just have to learn, like using `(setv var value)` to do assignment, or the fact that `(for)` is an imperative loop while `(lfor)` is a list comprehension, but a little experimentation goes a long way and the docs are quite good.