Unexpected behavior of clear() after clone() in turtle.py module

Unexpected behavior report

Unexpected behavior description:

Hello, I recently started teaching Python. I found turtle module interesting and I'm planning to use the module for deeper understanding of loop, condition, and function. I tried to simplify some turtle examples, just to show how for loop works. I cloned Turtle object, moved the clones to initial position, and cleared all Turtles before start drawing. However, clear() method did not work as I expected. Here is the code that I used.

from turtle import *

t1 = Turtle()
t2 = t1.clone()

t1.forward(100)
t2.right(90)
t2.forward(100)

t2.clear()

I expected t2.clear() to clear the trace of the cloned Turtle. Instead, t2.clear() erased the trace of the original Turtle, where the trace was drawn after the cloning.

I wanted to know what is going on, so I read the definition of clear() method, and the method seemed to delete all items in self.items. Also, the source code of forward() used self.currentLineItem when drawing. So I tracked items and currentLineItem in my code. Here are the results of the tracking.

from turtle import *

#t1.currentLineItem, t1.items, t2.currentLineItem, t2.items

t1 = Turtle()   #1, [1], None, None

t2 = t1.clone() #2, [1,2], 3, [1,2]

t1.forward(100) #2, [1,2], 3, [1,2]
t2.right(90)    #2, [1,2], 3, [1,2]
t2.forward(100) #2, [1,2], 3, [1,2]

t2.clear()      #2, [1,2], 4, [4]

So, t2 drew lines in 3, however, because 3 is not in t2.items, t2.clear() does not delete 3. Also, t1 drew lines in 2, and, because 2 is in t2.items, t2.clear() delete 2.

I think that the items of the cloned Turtle should be [1,3] instead of [1,2] after clone() is called.

CPython versions tested on:

3.12

Operating systems tested on:

Windows

Linked PRs

• gh-126401
• gh-127189

Start with the turtle.py definitions of clone(), clear(), and forward(), then reproduce the issue's t1/t2 example and review linked PRs gh-126401 and gh-127189. Done means a cloned Turtle tracks and clears its own drawing without clearing the original Turtle's trace.