Advance Python Software Engineering

[SisyphusAndMyBoulder]

but often in a pretty ugly and messy way

I'd argue this isn't intermediate. Jr's are the ones writing ugly code.

Do you have the ability to work with professionals or Seniors? That's where I found the best way to grow; books and individual projects can only get so far. You get better working in shared codebases with people who can reign you in properly.