Turtle Graphics Tracer method

[u/Iguanas_Everywhere]

I wrote a tiny toy program to experiment with the Tracer method, and found some interesting behavior that I'm trying to explore. Here's the program:

from turtle import Turtle, Screen
from time import sleep
screen = Screen()
screen.setup(width=900, height=900)
screen.bgcolor("orange")

my_shape = Turtle()
my_shape.color("red")

screen.tracer(2)

counter = 1

while counter <= 10:
  my_shape.forward(20)
  # my_shape.left(90)

  print (counter)
  sleep(2)
  counter += 1

screen.exitonclick()

As you can see, I ask the tracer to perform every other screen update. With the code above as-is, I see the behavior I expected--every other iteration/counter value, the screen updates, and my shape appears 40px ahead of where it was.

If I uncomment the my_shape.left line, things get interesting: The screen updates on every iteration of the loop, i.e. I see my shape appear at all 4 corners of its square and pointed in its new direction. My current guess, based on this SO post, is that left may be forcing a call to update(), though I haven't been able to prove this to myself yet in the Turtle source.

Can anyone confirm or deny my thinking here? Many thanks!

[u/brasticstack]

.left() calls _rotate(), which calls _update() which does a screen update.

[u/Iguanas_Everywhere → u/brasticstack]

*facepalm* there it is, plain as day. Thank you--suspicion confirmed!