For the record, some helpful resources:

ECMA-404 (the ECMA standardization of JSON): http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-404.pdf

RFC 8259 (current RFC for JSON): https://tools.ietf.org/html/rfc7159. (I mistakenly referred to RFC 7159 in a previous comment, but that's obsoleted by RFC 8259; however, none of the language around infinities and nans has changed, and none of the current errata to RFC 8259 have any impact on infinity or nan encoding.)

This Stack Overflow question and its answers contain some interesting discussion and links: https://stackoverflow.com/questions/1423081/json-left-out-infinity-and-nan-json-status-in-ecmascript 

Essentially, there's no good answer here: standard JSON simply can't encode infinities and NaNs. Absent a fix for the standard itself, both Python and ECMAScript end up papering over that fact. Unfortunately from an interoperability point of view, they do so in different ways - Python effectively extends the JSON spec in such a way that it produces invalid JSON by default; ECMAScript converts all of Infinity, -Infinity, NaN and null to the exact same JSON string, producing valid JSON but losing the ability to restore the original values from their JSON representations.

FWIW, Python's solution to this problem is (whether by accident or design I'm not sure) forward-looking in the sense that it's compatible with JSON 5: https://spec.json5.org