René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Harden ttk/tkinter GUI tests against display scaling (DPI)","articleBody":"Several `test_ttk` and `test_tkinter` GUI tests probe widget elements at fixed pixel coordinates (typically `(5, 5)`) or scan a fixed pixel range (e.g. `range(5, 100, 5)`, `range(0, 100, 10)`). ttk element geometry — tab padding, the focus ring, trough insets, row height — scales with the display DPI (`tk scaling`), so a fixed pixel that lands on the intended element at a normal scaling lands on a different element, or misses it entirely, at a high DPI.\n\nThis produces two failure modes:\n\n- The test fails outright at high DPI (e.g. `NotebookTest.test_traversal` clicked `(5, 5)`, which no longer lands on a tab at scaling 2.0).\n- The test passes *by accident* — its assertion accepts `''` (the \"nothing here\" result), so it never actually exercises the behaviour it claims to (e.g. `ScaleTest.test_identify` always identified `''` at `(5, 5)`; the darwin branch of `test_traversal` asserted `identify(5, 5) == ''`).\n\nBoth are latent: they surface on Retina/HiDPI macOS (Homebrew Tk 9, scaling 2.0) and any X11 display with a high `-dpi`.\n\nFix: compute probe coordinates from the widget's own realized geometry instead of hardcoding pixels — `ttk::notebook index @x,y` for a point guaranteed to lie on a given tab, `winfo_width()/winfo_height()` centre for Entry, `Scale.coords()` for the trough, and scanning the real `winfo_height()` for Treeview rows. This makes the tests position-, theme-, platform- and scaling-agnostic, and removes the darwin coordinate special-cases.\n\nTest-only change. Affects `test_ttk` (`EntryTest.test_identify`, `NotebookTest.test_tab_identifiers`, `NotebookTest.test_traversal`, `TreeviewTest.test_tag_bind`) and `test_tkinter` (`ScaleTest.test_identify`). Verified across scaling 1–6 (DPI 72–432) on Tk 8.6.17 and 9.0.3.\n\n\n\u003c!-- gh-linked-prs -->\n### Linked PRs\n* gh-153717\n* gh-153737\n* gh-153738\n* gh-153743\n\u003c!-- /gh-linked-prs -->\n","author":{"url":"https://github.com/serhiy-storchaka","@type":"Person","name":"serhiy-storchaka"},"datePublished":"2026-07-14T19:21:58Z","url":"https://github.com/python/cpython/issues/153716"}