From fb9e7b58fdfa921677e641d9f71aa17ff92bfe80 Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Sat, 10 Oct 2026 01:28:39 +0200
Subject: [PATCH 1/2] Add PyUnicodeWriter_WriteUCS4() function

---
 docs/api.rst                        |  7 ++++++-
 docs/changelog.rst                  |  1 +
 pythoncapi_compat.h                 | 15 +++++++++++++++
 tests/test_pythoncapi_compat_cext.c | 11 ++++++++++-
 4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/docs/api.rst b/docs/api.rst
index 7a5ba70..b0ff7d2 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -193,6 +193,12 @@ Python 3.14
 
    Not available on the limited C API.
 
+.. c:function:: int PyUnicodeWriter_WriteUCS4(PyUnicodeWriter *writer, const Py_UCS4 *ucs4, Py_ssize_t size)
+
+   See `PyUnicodeWriter_WriteUCS4() documentation <https://docs.python.org/dev/c-api/unicode.html#c.PyUnicodeWriter_WriteUCS4>`__.
+
+   Not available on the limited C API.
+
 .. c:function:: int PyUnicodeWriter_WriteUTF8(PyUnicodeWriter *writer, const char *str, Py_ssize_t size)
 
    See `PyUnicodeWriter_WriteUTF8() documentation <https://docs.python.org/dev/c-api/unicode.html#c.PyUnicodeWriter_WriteUTF8>`__.
@@ -338,7 +344,6 @@ Not supported:
 * ``PyInitConfig_SetStrList()``
 * ``PyType_GetBaseByToken()``
 * ``PyUnicodeWriter_DecodeUTF8Stateful()``
-* ``PyUnicodeWriter_WriteUCS4()``
 * ``Py_InitializeFromInitConfig()``
 
 
diff --git a/docs/changelog.rst b/docs/changelog.rst
index 2d9f1b7..db7fc9f 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -1,6 +1,7 @@
 Changelog
 =========
 
+* 2026-10-10: Add ``PyUnicodeWriter_WriteUCS4()`` function.
 * 2026-10-08: Add support for the limited C API 3.2.
 * 2026-10-08: Add functions:
 
diff --git a/pythoncapi_compat.h b/pythoncapi_compat.h
index 735ab24..4d5bf84 100644
--- a/pythoncapi_compat.h
+++ b/pythoncapi_compat.h
@@ -1620,6 +1620,21 @@ PyUnicodeWriter_WriteSubstring(PyUnicodeWriter *writer, PyObject *str,
                                            start, end);
 }
 
+static inline int
+PyUnicodeWriter_WriteUCS4(PyUnicodeWriter *writer,
+                          const Py_UCS4 *ucs4, Py_ssize_t size)
+{
+    PyObject *str = PyUnicode_FromKindAndData(PyUnicode_4BYTE_KIND,
+                                              ucs4, size);
+    if (str == NULL) {
+        return -1;
+    }
+
+    int res = _PyUnicodeWriter_WriteStr((_PyUnicodeWriter*)writer, str);
+    Py_DECREF(str);
+    return res;
+}
+
 static inline int
 PyUnicodeWriter_Format(PyUnicodeWriter *writer, const char *format, ...)
 {
diff --git a/tests/test_pythoncapi_compat_cext.c b/tests/test_pythoncapi_compat_cext.c
index 55e4e17..9a97f7d 100644
--- a/tests/test_pythoncapi_compat_cext.c
+++ b/tests/test_pythoncapi_compat_cext.c
@@ -1899,6 +1899,7 @@ test_unicodewriter(PyObject *Py_UNUSED(self), PyObject *Py_UNUSED(args))
         return NULL;
     }
     int ret;
+    const Py_UCS4 ucs4[] = {'u', 'c', 's', '4'};
 
     // test PyUnicodeWriter_WriteStr()
     PyObject *str = PyUnicode_FromString("var");
@@ -1940,6 +1941,14 @@ test_unicodewriter(PyObject *Py_UNUSED(self), PyObject *Py_UNUSED(args))
         goto error;
     }
 
+    // test PyUnicodeWriter_WriteUCS4()
+    if (PyUnicodeWriter_WriteUCS4(writer, ucs4, Py_ARRAY_LENGTH(ucs4)) < 0) {
+        goto error;
+    }
+    if (PyUnicodeWriter_WriteChar(writer, ' ') < 0) {
+        goto error;
+    }
+
     // test PyUnicodeWriter_WriteRepr()
     str = PyUnicode_FromString("repr");
     if (str == NULL) {
@@ -1958,7 +1967,7 @@ test_unicodewriter(PyObject *Py_UNUSED(self), PyObject *Py_UNUSED(args))
         if (result == NULL) {
             return NULL;
         }
-        const char *expected = "var=long non-ASCII valu\xC3\xA9 'repr'<NULL>";
+        const char *expected = "var=long non-ASCII valu\xC3\xA9 ucs4 'repr'<NULL>";
         assert(PyUnicode_EqualToUTF8(result, expected));
         Py_DECREF(result);
     }

From f6043ab5f4e09b6dd54274a9f643d67847edce0b Mon Sep 17 00:00:00 2001
From: Victor Stinner <vstinner@python.org>
Date: Sat, 10 Oct 2026 01:33:43 +0200
Subject: [PATCH 2/2] Update doc

---
 docs/api.rst | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/docs/api.rst b/docs/api.rst
index b0ff7d2..13a9d1b 100644
--- a/docs/api.rst
+++ b/docs/api.rst
@@ -2,12 +2,12 @@
 pythoncapi_compat.h API
 +++++++++++++++++++++++
 
-The ``pythoncapi_compat.h`` header file provides implementations of recent
-functions for old Python versions.
+The ``pythoncapi_compat.h`` header file provides implementations of around 150
+recent functions for old Python versions.
 
 Supported Python versions:
 
-* Python 3.6 - 3.15
+* Python 3.6 - 3.16
 * PyPy 3.6 - 3.12
 
 C++03 and C++11 are supported on Python 3.6 and newer.