why does abs() function works for the position coordinate in Python?

Question

I am looking at the Python document for turtle graphics, it has an example on drawing the turtle star. the program is as follow:

from turtle import *
color('red', 'yellow')
begin_fill()
while True:
    forward(200)
    left(170)
    if abs(pos()) < 1:
        break
end_fill()
done()

I don't understand why the abs(pos()) works? The abs() function takes a single argument, but the pos() function returns a position (x,y) coordinate. I know the program works, just don't understand why. I tried it on the Python interpreter with abs((-0.00,0.00)), it returns error. Please help!

Answer 1

pos() returns a turtle.Vec2D, not a tuple. You can make abs() work for any type by implementing __abs__(). In the case of turtle, __abs__() returns (self[0]**2 + self[1]**2)**0.5 as per the turtle source code here.

Answer 2

The pos() is not returning a tuple with x and y coordinate, instead it is returning an object of type turtle.Vec2D, this can be verified using:

>>> type(pos())
>>> turtle.Vec2D

Further if you run dir(pos()) you may get:

['__abs__', '__add__', ... '__class__','count', 'index', 'rotate']

So the turtle.Vec2D object has its own __abs__ implementation, but a generic tuple has no such implementation.