GeezerVison

Thanks for the PR — the FocusIn traceback is real, but the fallback return self.mtime runs too early in one case.

EditorWindow.__init__ calls io.set_filename(filename) for a filename that does not exist yet (python -m idlelib new.py), which goes set_saved(True) → last_mtime() before self.mtime is assigned at line 315. On main that already aborts IDLE at startup with FileNotFoundError (a regression from gh-94523, shipped in 3.13.15, 3.14.7 and 3.15.0b1); with this patch it aborts with AttributeError: 'EditorWindow' object has no attribute 'mtime' instead.

last_mtime() should return None when there is no file or it cannot be stat'ed (not 0, which is a valid mtime on filesystems that do not keep timestamps). A new file then opens with mtime = None, and a file that is created by another program after opening still triggers the existing reload prompt.

When the file was there and is now gone (self.mtime is not None and mtime is None), "modified by another program, reload?" is the wrong question — reloading can only fail. Ask instead what to do with the buffer: Close, Save As or Ignore, with Save As as the default. tkinter.simpledialog.SimpleDialog(..., buttons=('Close', 'Save As', 'Ignore'), default=1, cancel=2) gives such a box; .go() returns the button index. Close → self.close(). Save As → self.io.save_as(event). Ignore → set self.mtime = None and self.set_saved(False), so the window is marked as unsaved but the question is not repeated on the next FocusIn.

This is an approximate plan; details can be changed later.

Please add a test for the not-yet-existing filename (a SimpleNamespace stub without mtime is enough to catch the AttributeError), expect None in test_deleted_file_does_not_raise, and tests for the deleted-file branch with the dialog mocked.

Two smaller things: the NEWS file belongs in Misc/NEWS.d/next/IDLE/, not Library/, and open(p, 'w').close() in the test can be Path(p).touch() or a with.

Thanks, this works for me now: starting with a not yet existing file, Ignore, reload after the file is recreated, Close. One remaining problem with a cancelled Save As, see the comment.

Found one more case: modify the file, delete it, get the focus back, choose Close. See the comment.

Thank you for your update.

test_deleted_file_returns_none and test_not_yet_created_filename are the same test.

Optional nits: the new tests could use os_helper.temp_dir() and os_helper.create_empty_file() instead of tempfile and pathlib.

I'm merging as is. Tests can be edited later.