Read def? What the point of that? You might say "def" when you see it, but you think of the concept of a function. You should be translating fn to "function" in your head or if you speak it out loud, the same way you say "plus" when you see +. How do you "read" + otherwise? It's the same for every mathematical symbol, since there is no actual way to read them, since they communicate a concept that you most likely translate into your own language in your head.