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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"curses: detect optional functions with configure probes instead of assuming ncurses","articleBody":"Several functions in `Modules/_cursesmodule.c` are called unconditionally or gated only by the ncurses-specific `NCURSES_EXT_FUNCS` macro. Both break building or using the module against curses implementations other than ncursesw — narrow (non-wide) ncurses, and third-party curses such as NetBSD curses — even when the library provides the function.\n\n**Unconditionally-called functions that aren't universally present** (no `HAVE_CURSES_*` guard, so a library lacking them fails to link):\n\n- `scr_dump`/`scr_restore`/`scr_init`/`scr_set` — the whole family is absent from NetBSD curses.\n- `key_defined` — absent from NetBSD curses (which has `define_key`/`keyok`).\n- `term_attrs` — the X/Open *wide* attribute query, present only in `libncursesw`, so missing from a narrow `-lncurses` build.\n\n**Functions gated by `NCURSES_EXT_FUNCS`** that NetBSD implements without defining that macro, so the module silently drops them:\n\n- `define_key`, `keyok`, `set_escdelay`, `set_tabsize`, `get_escdelay`, `get_tabsize`.\n\n**Proposed change:** detect each with a configure capability probe and gate on `HAVE_CURSES_*`.\n\n- `PY_CHECK_CURSES_FUNC` probes for `scr_dump` (one probe gates the inseparable family), `key_defined`, `term_attrs`, `define_key`, `keyok`, `set_escdelay`, `set_tabsize`.\n- `get_escdelay`/`get_tabsize` read the `ESCDELAY`/`TABSIZE` *variables*, which some libraries declare as `extern int` rather than macros, so a function probe doesn't fit. Add a small `PY_CHECK_CURSES_VAR` macro (tests that `int x = ESCDELAY;` compiles) and gate the getters on `HAVE_CURSES_ESCDELAY`/`HAVE_CURSES_TABSIZE`.\n\nNone of these are in X/Open Curses; they are ncurses extensions (NetBSD provides compatible ones), so capability-gating is the correct treatment, and a probe is more portable than conditioning on `NCURSES_VERSION`.\n\nNo behaviour change on standard ncursesw (all macros defined). `test_curses` passes and is refleak-clean on ncursesw, narrow ncurses, and NetBSD curses, under UTF-8 and 8-bit locales. `test_env_queries` calls `curses.term_attrs()` unconditionally and needs a `hasattr` guard for the narrow case.\n\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-152504\n* gh-152589\n* gh-152602\n* gh-152603\n* gh-152705\n* gh-152707\n* gh-152734\n* gh-152735\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/serhiy-storchaka","@type":"Person","name":"serhiy-storchaka"},"datePublished":"2026-06-28T16:14:54.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/152502/cpython/issues/152502"}