Method keyword_index

include/pybind11/pybind11.h:1385–1405

    }

    static ssize_t keyword_index(PyObject *haystack, char const *needle) {
        /* kwargs is usually very small (<= 5 entries).  The arg strings are typically interned.
         * CPython itself implements the search this way, first comparing all pointers ... which is
         * cheap and will work if the strings are interned.  If it fails, then it falls back to a
         * second lexicographic check. This is wildly expensive for huge argument lists, but those
         * are incredibly rare so we optimize for the vastly common case of just a couple of args.
         */
        auto n = PyTuple_GET_SIZE(haystack);
        auto s = reinterpret_steal<pybind11::str>(PyUnicode_InternFromString(needle));
        for (ssize_t i = 0; i < n; ++i) {
            if (PyTuple_GET_ITEM(haystack, i) == s.ptr()) {
                return i;
            }
        }
        for (ssize_t i = 0; i < n; ++i) {
            if (PyUnicode_Compare(PyTuple_GET_ITEM(haystack, i), s.ptr()) == 0) {
                return i;
            }
        }
        return -1;
    }
};

PYBIND11_NAMESPACE_BEGIN(detail)