I really like Python but I think there's nothing wrong with continuing to learn Ruby and Rails. Be sure to learn both Ruby the language and Rails the framework, there's more to Ruby than Rails. You'll likely also want to at least get your toes wet with Javascript so you can write native code for the client side of the browser, while you're learning that you'll be comparing with what you've learned with Ruby and from your previous experience with Fortran.

After learning those picking up Python will be fairly easy. Again, you'll be comparing with what you know, finding differences and similarities.

Don't worry too much about finding the perfect language, it doesn't exist. Spend your time building nice things in languages and frameworks that are good at at what they do. Be ready to try new things, you might like them, they might work well for a particular task or have a great ecosystem to accomplish specific things.