Show me a tutorial on Python graphics on OS X that doesn't require installing an external library or learning about a really complicated graphics framework (Quartz 2D) and I'll believe what you just wrote.
Your requirement that there be no external libraries is unfair. It's perfectly valid for a tutorial to start with "Download this package and run the installer," which is easier than any actual programming the reader might do.
There are plenty of great tutorials for PyGame and pyglet. The main issue is that you have to open a terminal.
If you look past Python, Scratch provides a very low barrier to entry for this sort of thing.
Your requirement that there be no external libraries is unfair.
If the question being discussed is "How likely is an 8-year-old to randomly discover programming", it's not unfair in the slightest. Installation of anything is a huge barrier to discoverability.
Random discovery is so difficult. If only there was an engine of some sort that we could search things with. We could call this engine of search - Bing!
Very well. See http://cs.gettysburg.edu/~tneller/resources/k12/index.html for a tutorial that demonstrates the use of the 'turtle' built in module in python. Turtle has a long history of being a simple graphical environment to introduce programming to young individuals, and that hasn't changed over the years. It would meet the original post author's requirements for graphing those simple functions.
Assuming you are targeting those -slightly- older, pyglet would offer an incredibly simple way to progress, but would require you download one library, which I feel is a very reasonable requirement.
Apple basic graphics was one of two commands:
GR or HGR