I want to code whiteboard program so I want to change shape of turtle to pen.
I wanna know Do we have something in turtle to add further - like pen - shape in turtle.shape()?
and if we have it, how can we add it?
The key to adding a new turtle cursor shape is the screen method register_shape() (aka addshape()). You can define the new shape either using polygons (individual or multiple) or an image file (traditionally a *.GIF but more recently also *.PNG, depending on the underlying version of tkinter).
Once a shape is registered, it can be used with the turtle shape() method to change the cursor to the new shape. Based on the turtle documentation:
from turtle import Screen, Turtle
screen = Screen()
screen.register_shape("custom.gif")
turtle = Turtle()
turtle.shape("custom.gif")
However, images don't rotate with the turtle. For that, you can define a polygon-based shape:
screen.register_shape("right_triangle", ((-10, 10), (-10, -10), (10, -10)))
turtle = Turtle()
turtle.shape("right_triangle")
Though the polygon image might not be oriented the way you expect so you may need to rotate your turtle or adjust your polygon coordinates.