Apply suggestions from code review

Author: asvetlov

Lib/asyncio/locks.py

@@ -489,7 +489,8 @@ def __init__(self, parties):
         self._parties = parties
         self._state = _BarrierState.FILLING
         self._count = 0       # count tasks in Barrier
-        self._index = self._parties - 1 # index number returned when barrier drains
+        # index number returned when barrier drains 
+        self._index = self._parties - 1 
 
     def __repr__(self):
         res = super().__repr__()
@@ -523,7 +524,7 @@ async def wait(self):
                 else:
                     await self._wait()
                 index = self._index
-                self._index = (self._index + 1) % self.parties
+                self._index = (self._index + 1) % self._parties
                 return index
             finally:
                 self._count -= 1
@@ -571,7 +572,7 @@ def _exit(self):
         if self._count == 0:
             if self._state in (_BarrierState.RESETTING, _BarrierState.DRAINING):
                 self._state = _BarrierState.FILLING
-                self._index = self.parties - 1
+                self._index = self._parties - 1
             self._cond.notify_all()
 
     async def reset(self):
@@ -587,7 +588,7 @@ async def reset(self):
                     self._state = _BarrierState.RESETTING
             else:
                 self._state = _BarrierState.FILLING
-                self._index = self.parties - 1
+                self._index = self._parties - 1
             self._cond.notify_all()
 
     async def abort(self):

Lib/test/test_asyncio/test_locks.py

@@ -1850,5 +1850,6 @@ async def coro():
         self.assertEqual(sorted(results), list(range(self.N)))
         self.assertEqual(barrier.n_waiting, 0)
 
+
 if __name__ == '__main__':
     unittest.main()

Misc/NEWS.d/next/Library/2026-10-07-10-59-27.gh-issue-155233.YGuQGK.rst

@@ -1 +1 @@
-Fix the returned value of the :meth:`asyncio.Barrier.wait`. This value is now calculated on demand during the *draining* phasis.
+Fix :meth:`asyncio.Barrier.wait` returning duplicate indices when a waiting task is cancelled before the barrier is released.```