gh-50966: Fix unbounded recursion in turtle drag handlers#152626
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serhiy-storchaka merged 1 commit intoJun 30, 2026
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TurtleScreenBase._update() redraws with cv.update(), which also reprocesses input events, so a handler that moves the turtle (such as screen.ondrag(turtle.goto)) reenters _update() for every queued event until the interpreter crashes. A reentrant _update() now only flushes drawing with update_idletasks(). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
serhiy-storchaka
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needs backport to 3.13
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Thanks @serhiy-storchaka for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13, 3.14, 3.15. |
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GH-152657 is a backport of this pull request to the 3.15 branch. |
bedevere-app
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needs backport to 3.15
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Sorry, @serhiy-storchaka, I could not cleanly backport this to |
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GH-152658 is a backport of this pull request to the 3.14 branch. |
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…152626) (GH-152657) TurtleScreenBase._update() redraws with cv.update(), which also reprocesses input events, so a handler that moves the turtle (such as screen.ondrag(turtle.goto)) reenters _update() for every queued event until the interpreter crashes. A reentrant _update() now only flushes drawing with update_idletasks(). (cherry picked from commit 6f103fa) Co-authored-by: Serhiy Storchaka <storchaka@gmail.com> Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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GH-152667 is a backport of this pull request to the 3.13 branch. |
serhiy-storchaka
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Jun 30, 2026
…152626) (GH-152658) TurtleScreenBase._update() redraws with cv.update(), which also reprocesses input events, so a handler that moves the turtle (such as screen.ondrag(turtle.goto)) reenters _update() for every queued event until the interpreter crashes. A reentrant _update() now only flushes drawing with update_idletasks(). (cherry picked from commit 6f103fa) Co-authored-by: Serhiy Storchaka <storchaka@gmail.com> Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
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turtle.TurtleScreenBase._update()redraws by callingcv.update(), which also reprocesses pending input events.When a mouse handler moves the turtle — the canonical example being
screen.ondrag(turtle.goto)— the move triggers another_update(), whosecv.update()dispatches the next queued motion event and reenters the handler.With a continuous drag this recurses without bound (each level adds Python and Tcl C-stack frames), eventually crashing the interpreter (
Tcl_Panic/ segfault).Guard
_update()so that a reentrant call only flushes pending drawing withupdate_idletasks()instead of reprocessing input, turning the recursion into bounded iteration.All drag callbacks still run (the turtle still follows the cursor); the non-reentrant path is unchanged.
Verified with a reproduction (reentrancy depth drops from dozens to 2 for a burst of queued drag events, all callbacks still processed) and a fast non-GUI regression test.