is there any way to pass a javascript value back to python without calling the page with parameters?

I have created a dropdown menu using a python call to a WMS server. I'd like to create another dropdown menu based on the the first menu choice. I can't do a normal dynamic dropdown menu because I have to do another python wms call based on the first menu choice.

I'd like to do the first call, read the menu choice, do the next call and create a new dropdown. I figure I'd do the first call in python, read the choice in javascript, do the second call in python then read the second choice and do more calls in python. All without doing a page call...

Use Ajax calls from the JavaScript to call the Python code.

I've never used Ajax. is there anywhere you can point me to such that I can actually learn how to use Ajax calls for this ? (or post some code snippet?) Thanks a million.