But replace the last line with 3+j["foo"] in python (and respectively, echo (3+j["foo"]) in Nim), and the Python prints 45 whereas the Nim compiler greets you with ~40 lines of output asking you what exactly you meant.

Just to clarify: I'm not complaining. I'm happy that the compiler bugs you to do 3+int(j["foo"]) if you're going to treat it as an int. But I don't consider Nim a statically typed Python.

(Also: am a very satisfied owner of a dead-tree version of the Nim book. Thanks! Highly recommended. And dom96 is awesome in general)