From 82f3279ee9028bcd32d091f5a57acce358ee2abf Mon Sep 17 00:00:00 2001
From: Aarni Koskela <akx@iki.fi>
Date: Mon, 27 Oct 2025 13:32:13 +0200
Subject: [PATCH] Add C implementation of UUID stringification

---
 Lib/test/test_uuid.py                         |  4 ++
 Lib/uuid.py                                   |  6 +++
 ...-10-27-13-17-17.gh-issue-131196.tYkQbd.rst |  2 +
 Modules/_uuidmodule.c                         | 45 ++++++++++++++++---
 4 files changed, 51 insertions(+), 6 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2025-10-27-13-17-17.gh-issue-131196.tYkQbd.rst

diff --git a/Lib/test/test_uuid.py b/Lib/test/test_uuid.py
index 33045a78721aac..75a90f7776be02 100755
--- a/Lib/test/test_uuid.py
+++ b/Lib/test/test_uuid.py
@@ -224,6 +224,10 @@ def test_UUID(self):
                       self.uuid.UUID(urn)]:
                 # Test all conversions and properties of the UUID object.
                 equal(str(u), string)
+                if hasattr(self.uuid, "_c_uuid_str_method"):
+                    # If we have the C accelerator, test both implementations.
+                    equal(self.uuid._py_uuid_str_method(u), string)
+                    equal(self.uuid._c_uuid_str_method(u), string)
                 equal(int(u), integer)
                 equal(u.bytes, bytes)
                 equal(u.bytes_le, bytes_le)
diff --git a/Lib/uuid.py b/Lib/uuid.py
index c0150a59d7cb9a..887e6e1fd046d8 100644
--- a/Lib/uuid.py
+++ b/Lib/uuid.py
@@ -635,6 +635,12 @@ def _netstat_getnode():
     _generate_time_safe = getattr(_uuid, "generate_time_safe", None)
     _has_stable_extractable_node = _uuid.has_stable_extractable_node
     _UuidCreate = getattr(_uuid, "UuidCreate", None)
+    _uuid_int_to_str = getattr(_uuid, "uuid_int_to_str", None)
+    _py_uuid_str_method = UUID.__str__
+    if _uuid_int_to_str is not None:
+        def _c_uuid_str_method(self):
+            return _uuid_int_to_str(self.int)
+        UUID.__str__ = _c_uuid_str_method
 except ImportError:
     _uuid = None
     _generate_time_safe = None
diff --git a/Misc/NEWS.d/next/Library/2025-10-27-13-17-17.gh-issue-131196.tYkQbd.rst b/Misc/NEWS.d/next/Library/2025-10-27-13-17-17.gh-issue-131196.tYkQbd.rst
new file mode 100644
index 00000000000000..63d02b2a6b0a03
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-10-27-13-17-17.gh-issue-131196.tYkQbd.rst
@@ -0,0 +1,2 @@
+Improve performance of :meth:`uuid.UUID.__str__ <object.__str__>` by adding
+a C implementation in _uuidmodule.
diff --git a/Modules/_uuidmodule.c b/Modules/_uuidmodule.c
index c31a7e8fea5608..685d9e96b88fe9 100644
--- a/Modules/_uuidmodule.c
+++ b/Modules/_uuidmodule.c
@@ -3,13 +3,9 @@
  * DCE compatible Universally Unique Identifier library.
  */
 
-// Need limited C API version 3.13 for Py_mod_gil
-#include "pyconfig.h"   // Py_GIL_DISABLED
-#ifndef Py_GIL_DISABLED
-#  define Py_LIMITED_API 0x030d0000
-#endif
-
+#define Py_BUILD_CORE_MODULE
 #include "Python.h"
+#include "pycore_long.h"  // _PyLong_AsByteArray
 #if defined(HAVE_UUID_H)
   // AIX, FreeBSD, libuuid with pkgconf
   #include <uuid.h>
@@ -90,6 +86,42 @@ py_windows_has_stable_node(void)
 }
 #endif /* MS_WINDOWS */
 
+static PyObject *
+py_uuid_int_to_str(PyObject *Py_UNUSED(context), PyObject *uuid_int)
+{
+    if (!PyLong_Check(uuid_int)) {
+        PyErr_SetString(PyExc_TypeError, "uuid_int must be an integer");
+        return NULL;
+    }
+
+    unsigned char bytes[16];
+    if (_PyLong_AsByteArray((PyLongObject *)uuid_int, bytes, 16, 0, 0, 1) < 0) {
+        return NULL;
+    }
+
+    PyObject *result = PyUnicode_New(36, 127);
+    if (result == NULL) {
+        return NULL;
+    }
+    assert(PyUnicode_KIND(result) == PyUnicode_1BYTE_KIND);
+    Py_UCS1 *str = PyUnicode_1BYTE_DATA(result);
+    static const Py_UCS1 hex_digits[] = "0123456789abcdef";
+
+    int pos = 0;
+    for (int i = 0; i < 16; i++) {
+        if (i == 4 || i == 6 || i == 8 || i == 10) {
+            str[pos++] = '-';
+        }
+        unsigned char byte = bytes[i];
+        str[pos++] = hex_digits[byte >> 4];
+        str[pos++] = hex_digits[byte & 0x0f];
+    }
+#ifdef Py_DEBUG
+    assert(pos == 36);
+    assert(_PyUnicode_CheckConsistency(result, 1));
+#endif
+    return result;
+}
 
 static int
 uuid_exec(PyObject *module)
@@ -129,6 +161,7 @@ static PyMethodDef uuid_methods[] = {
 #if defined(MS_WINDOWS)
     {"UuidCreate", py_UuidCreate, METH_NOARGS, NULL},
 #endif
+    {"uuid_int_to_str", py_uuid_int_to_str, METH_O, NULL},
     {NULL, NULL, 0, NULL}           /* sentinel */
 };