Ask HN: What Technologies to Learn in 2020?
Learn how to really use a relational database, relational data modeling, and SQL.  Not knowing of their capabilities may lead you to unnecessarily complicating your tech stack.  You can go a really long way with just this domain of expertise.  From there, do the same with whatever key-value store interests you (for me, it's Redis).  Python isn't known for high performance but when a django web app uses a cache and relational database effectively, it can achieve a very acceptable peformance.  Case in point:  the Zulip chat platform:  zulipchat.com.Aside from the database domain, I really enjoy using Rust and recommend it as the next language for anyone to learn, but only after taking time for in-depth relational database training. :).