I currently know a working knowledge of Python and some related libraries (including the included-with-Python SQLite) for the purpose of making desktop applications.
I would now like to start to make "web applications". By this, I mean that whatever is on the desktop application will be done by visiting a website...so the web page will have all the same sorts of widgets found in desktop apps (buttons, pulldowns, textboxes, etc).
I am not interested in making just static web sites or online magazines or things like that.
I'm also open to the idea of using a different programming language than Python, though I like it and would prefer to keep using it. I'd like to start simple and make small toy apps just to get the basic ideas, and then build from there.
EDIT FOR SPECIFIC QUESTION: What are the minimum tools/services will I need to get/learn to produce web apps (as defined above) using Python?
EDIT 2: I'm removing references to SaaS. Let's just call it a widget-using web app.