Nuke's in-built script editor is pretty swanky, to be perfectly honest. You get
as many lines as you want
some basic (good enough for most cases) syntax highlighting;
auto-completion and introspection (so. very. useful.) ;
block commenting;
block indent and dedent;
and it saves everything so you don't have to think about it too much!
For indenting by the way, python has a very strong code style which is where the four spaces thing comes from - https://www.python.org/dev/peps/pep-0008 - and it's particularly important in a language where whitespace is used to denote blocks of 'stuff'. It's a trade-off, but having lots of { and } floating around (e.g. C/C++) is nice and explicit.. but leads to some fun discussions around style, like say, here: https://en.wikipedia.org/wiki/Indenta...
(For what it's worth, if pressed, i probably would default to Stroustrup or K&R)