Coding for FICC & rates

Just interested to know more about the topic. On LinkedIn I've seen far too many analysts/associates at top AMs listing in their job description their coding skills in fixed income, rates derivatives (eg swaptions), currencies, and commodities valuation. I'm familiar with the products and how to value them using simple contrived examples on paper, but I don't know where to start with coding. 

I'm not from a quant background so I'm looking to strictly teach myself. Would really appreciate it if someone were to touch down on this topic. 


Edit. Lol why tf does this site include a US-midwest tag on every post? I'm based in London, also from a low-tier semi target.