> For the best of my (limited) knowledge, there's currently
> no arc() function in module turtle.

circle() takes a second argument called "extent":

   circle(200, 90)    # draw 90° of a circle of radius 200

FWIW, searching the turtle documentation page for "arc" immediately finds the two argument form of circle, so I don't think there is a discoverability problem.

Suggestion for Yehuda:  Consider driving the turtle module from IPython.  It has an "%autocall" mode that automatically adds parentheses.  For example:

    forward 100
    right 90

gets automatically transformed to:
    forward(100)
    right(90)

FWIW, I concur with Nick that we shouldn't add a new circle function centered on the turtle.  He was correct that this would make a great exercise.   More importantly, making the module bigger doesn't make it easier to use (see https://en.wikipedia.org/wiki/Overchoice ).  You've already indicated that you don't yet know the full API and haven't found essential tools like the two argument form of circle(), so making the API bigger would likely have made the discoverability problem worse.

At this point, I think we should close this tracker issue:

* It's not easily possible to make "rt" generate an error message
* Circle centered on a turtle is best left as an exercise
* arc() is already present in the two argument form of circle()

One other thought:  The Python API was based on other turtle implementations, so the API is probably mostly already where it should be.