Closes#29688

Objects without a parent are not necessarily cleaned up in PyQt when their reference count reaches zero, and must be explicitly cleaned up withdeleteLater()

This prevents the notifier firing after the signal handling was supposed to have been cleaned up, which can cause spurious errors to be printed if it runs upon further interrupts or at interpreter shutdown.

I've tested this on Linux with Python 3.13, using both of

matplotlib.use('QtAgg')matplotlib.use('Qt5Agg')

Previously, running the following withpython -i script.py:

importmatplotlib.pyplotaspltplt.plot([1,2,3], [4,5,6])plt.show()

and then pressing ctrl-C in the terminal whilst the figure was shown, would cause a traceback and error messageOSError: [Errno 9] Bad file descriptor to be printed as the interpreter exited (by e.g. subsequently pressing ctrl-D), and at least for me, cause the controlling terminal to exit for some reason.

After this change interpreter shutdown appears clean.

Similarly, as in the original bug report, runningipython and then entering in the REPL:

import matplotlib.pyplot as pltplt.plot([1, 2, 3],[5, 4, 6])plt.pause(10)

and pressing ctrl-C would result in an infinite loop ofOSError: [Errno 9] Bad file descriptor error messages, and with this change results in a singleKeyBoardInterrupt traceback as expected.

PR checklist

• "closes #0000" is in the body of the PR description tolink the related issue
• new and changed code istested
  - []Plotting related features are demonstrated in anexample N/A
  - [ ]New Features andAPI Changes are noted with adirective and release note N/A
  - [] Documentation complies withgeneral anddocstring guidelines N/A

I've checked the docs build and the tests run - one test fails:test_font_heuristica[pdf] but it fails regardless of this change. I have only tested on Linux with Python 3.13.3.