If the main criteria is to be similar to Ruby + Rails, Python + Django is the right way to go. Beyond the many similarities of Ruby and Python as languages, Django fills the niche for the Python web development ecosystem that Rails does for Ruby; a fully fleshed-out framework, which comes with batteries included.

Many people have had the experience of choosing a lightweight framework (Sinatra, Flask, etc.) and gradually needing more and more features from a heavier framework. Eventually you find that you wrote a poorly documented, poorly implemented version of Django or Rails, and bringing new people onto your team is now far harder than just finding people who've used a specific framework.