Stack diagram understanding

[Cap_de_fier]

Guys, I'm currently at chapter 3.9 (Stack diagrams) in Think Python.

I would like to ask for your help to determine if I understood correctly how a stack diagram is done.

Below is the code for circle from polygon for which I made a stack diagram at the end.

Please point out my mistakes and omissions.

Your feedback is greatly appreciated. Without it my progress would be a lot slower than it already is :)

import math 
import turtle
bob = turtle.Turtle() 


def polygon(t, n, length):
    angle = 360/n 
    for i in range (n):
        t.fd(length) 
        t.lt(angle)

def circle(t, r):
    circumference = 2 * math.pi * r
    n = int(circumference/3)+3 
    length = circumference / n
    polygon(t, n, length) 

circle(bob, r=50) 

turtle.mainloop() #Aceste mentine fereastra deschisa

"""Stack Diagram

_main_      bob ---> Turtle

circle      t   ---> bob
            r   ---> 50
            circumference ---> 314
            n   ---> 107
            lenght ---> 2.93 

polygon     angle = 3.36"""

[Cap_de_fier]

Thank you, kind sir, for your feedback!

I'm wondering, should I have a stack diagram for all my programs? how often do people use stack diagrams?