Just finished Python Programming - An Introduction to Computer Science. What would be a good next step?

First off, a HUGE thank you r/python for all of the suggestions from my last post. They really helped a lot with getting started. Especially the Thinking Like a Computer Scientist online book. Very, very useful!

Anyway, I just finished the book, and think I have a decent grasp on the basics, but I'm not sure where to go from here. What are the core things I need to learn next?

My interests lay in web development, mainly because I think that'd be a great way to 'get my hands dirty' and be able to see results. Longer term would be application development. Specifically... audio plugins.

So, any semi-intermediate book suggestions?