gh-118993: Use OS-generated UUIDs for uuid.uuid1() on Windows

Doc/library/uuid.rst

@@ -201,6 +201,11 @@ The :mod:`!uuid` module defines the following functions:
    If *node* or *clock_seq* exceed their expected bit count,
    only their least significant bits are kept.
 
+   .. versionchanged:: next
+      On Windows, when neither *node* nor *clock_seq* is given, the UUID is
+      now generated by the system ``UuidCreateSequential()`` function and
+      reported as safe by :attr:`UUID.is_safe`.
+
 
 .. function:: uuid3(namespace, name)
 

Lib/test/test_uuid.py

@@ -636,8 +636,17 @@ def test_uuid1_bogus_return_value(self):
             self.assertEqual(u.is_safe, self.uuid.SafeUUID.unknown)
             self.assertEqual(u.version, 1)
 
+    def test_uuid1_windows_safe(self):
+        if self.uuid._UuidCreate is None:
+            self.skipTest('requires _uuid.UuidCreate')
+        u = self.uuid.uuid1()
+        self.assertEqual(u.is_safe, self.uuid.SafeUUID.safe)
+        self.assertEqual(u.version, 1)
+        self.assertEqual(u.variant, self.uuid.RFC_4122)
+
     def test_uuid1_time(self):
         with mock.patch.object(self.uuid, '_generate_time_safe', None), \
+             mock.patch.object(self.uuid, '_UuidCreate', None), \
              mock.patch.object(self.uuid, '_last_timestamp', None), \
              mock.patch.object(self.uuid, 'getnode', return_value=93328246233727), \
              mock.patch('time.time_ns', return_value=1545052026752910643), \

Lib/uuid.py

@@ -729,16 +729,20 @@ def uuid1(node=None, clock_seq=None):
     address.  If 'clock_seq' is given, it is used as the sequence number;
     otherwise a random 14-bit sequence number is chosen."""
 
-    # When the system provides a version-1 UUID generator, use it (but don't
-    # use UuidCreate here because its UUIDs don't conform to RFC 4122).
-    if _generate_time_safe is not None and node is clock_seq is None:
-        uuid_time, safely_generated = _generate_time_safe()
-        try:
-            is_safe = SafeUUID(safely_generated)
-        except ValueError:
-            is_safe = SafeUUID.unknown
-        # The version field is assumed to be handled by _generate_time_safe().
-        return UUID(bytes=uuid_time, is_safe=is_safe)
+    # When the system provides a version-1 UUID generator, use it.
+    if node is clock_seq is None:
+        if _generate_time_safe is not None:
+            uuid_time, safely_generated = _generate_time_safe()
+            try:
+                is_safe = SafeUUID(safely_generated)
+            except ValueError:
+                is_safe = SafeUUID.unknown
+            # The version field is assumed to be handled by
+            # _generate_time_safe().
+            return UUID(bytes=uuid_time, is_safe=is_safe)
+        if _UuidCreate is not None:
+            uuid_bytes = _UuidCreate()
+            return UUID(bytes_le=uuid_bytes, is_safe=SafeUUID.safe)
 
     global _last_timestamp
     nanoseconds = time.time_ns()

Misc/NEWS.d/next/Library/2026-07-26-22-22-51.gh-issue-118993.U1adlE.rst

@@ -0,0 +1,4 @@
+On Windows, :func:`uuid.uuid1` now uses the system
+``UuidCreateSequential()`` function when neither *node* nor *clock_seq* is
+given, so concurrent processes no longer produce colliding UUIDs and the
+result is reported as safe by :attr:`uuid.UUID.is_safe`.