Scraper Google App Engine for Steam
Since you have the steam id from the service you can then make another request to their steam community page via the id.  From there you can use beautiful soup to return a dom to grab the required information for your project.
Now onto your question.  You can have all this happen within a request in a handler, if you are using a web framework such as Tornado, and the handler can return json in the page and you can render this json using your javascript code.
Look into a web framework for python such as Tornado or Django to help you with return and displaying the data.
So basically, at the moment, we are trying to write a basic HTML 5 page that, when you press a button, returns whether the user, on Steam, is in-game, offline, or online. We have looked at the Steam API, and to find this information, it requires the person's 64 bit ID (steamID64) and we, on the website, are only given the username. In order to find their 64 bit id, we have tried to scrape off of a website (steamidconverter.com) to get the user's 64 bit id from their username. We tried doing this through the javascript, but of course we ran into the cross domain block, not allowing us to access that data from our google App Engine website.
I have experience in Python, so I attempted to figure out how to get the HTML from that website (in the form of steamidconverter.com/(personsusername)) with Python. That was a success in scraping, thanks to another post on Stack Overflow.
BUT, I have no idea how to get that data back to the javascript and get it to do the rest of the work. I am stumped and really need help. This is all on google App Engine. All it is at the moment, is a button that runs a simple javascript that attempts to use JQuery to get the contents of the page back, but fails. I don't know how to integrate the two!
Please Help!