I have been working with Amazon API for several years and I will admit that they seem to try to hide what they are doing with their regular affiliate stuff, like Amazon Search, as if they don't want you to use the API or at least make it difficult.
So, in your affiliate dashboard, click the 'Product API' tab at the top.
Next, you will need to create your public and private keys. If those aren't created and set up, you won't be able to access the API. Also be aware that even though Amazon does have a RESTful API, it requires a callback, regardless of the language you use. (Unless you're going to use SOAP) Once those are created, it should open up some new options for you in you affiliate dashboard.
Finally, Amazon has code samples out the wazoo, but I cannot testify that either the Ruby or Python ones are any good (as I have done mine with cURL and php), but it should give you a good starting point anyway. Go here: http://aws.amazon.com/code/Product%20Advertising%20API?_encoding=UTF8&jiveRedirect=1
I do see python and ruby listed here in the code samples and docs. Be aware Amazon likes to change things frequently, sometimes without notice. But I did just notice while doing this a section about a new node js library for AWS...sweet. Amazon for all it bs does do a good job.