writing a minor mode

[R. Sean Bowman]

hello,

I use emacs to edit Python code, and I hate lines longer than 80
characters.  I'd like to write a minor mode that draws a vertical line or
darkens the character at the 80th spot, but I'm confused about how to do
that.  Should I use a bunch of overlays?  Is there some better way?  Any
help would be greatly appreciated.

Sean