bpo-24391: Better reprs for threading objects. (GH-20534)

Add reprs for Semaphore, BoundedSemaphore, Event, and Barrier.

Lib/test/lock_tests.py

@@ -455,6 +455,12 @@ class EventTests(BaseTestCase):
         with evt._cond:
             self.assertFalse(evt._cond.acquire(False))
 
+    def test_repr(self):
+        evt = self.eventtype()
+        self.assertRegex(repr(evt), r"<\w+\.Event at .*: unset>")
+        evt.set()
+        self.assertRegex(repr(evt), r"<\w+\.Event at .*: set>")
+
 
 class ConditionTests(BaseTestCase):
     """
@@ -802,6 +808,15 @@ class SemaphoreTests(BaseSemaphoreTests):
         sem.acquire()
         sem.release()
 
+    def test_repr(self):
+        sem = self.semtype(3)
+        self.assertRegex(repr(sem), r"<\w+\.Semaphore at .*: value=3>")
+        sem.acquire()
+        self.assertRegex(repr(sem), r"<\w+\.Semaphore at .*: value=2>")
+        sem.release()
+        sem.release()
+        self.assertRegex(repr(sem), r"<\w+\.Semaphore at .*: value=4>")
+
 
 class BoundedSemaphoreTests(BaseSemaphoreTests):
     """
@@ -816,6 +831,12 @@ class BoundedSemaphoreTests(BaseSemaphoreTests):
         sem.release()
         self.assertRaises(ValueError, sem.release)
 
+    def test_repr(self):
+        sem = self.semtype(3)
+        self.assertRegex(repr(sem), r"<\w+\.BoundedSemaphore at .*: value=3/3>")
+        sem.acquire()
+        self.assertRegex(repr(sem), r"<\w+\.BoundedSemaphore at .*: value=2/3>")
+
 
 class BarrierTests(BaseTestCase):
     """
@@ -1008,3 +1029,18 @@ class BarrierTests(BaseTestCase):
         b = self.barriertype(1)
         b.wait()
         b.wait()
+
+    def test_repr(self):
+        b = self.barriertype(3)
+        self.assertRegex(repr(b), r"<\w+\.Barrier at .*: waiters=0/3>")
+        def f():
+            b.wait(3)
+        bunch = Bunch(f, 2)
+        bunch.wait_for_started()
+        time.sleep(0.2)
+        self.assertRegex(repr(b), r"<\w+\.Barrier at .*: waiters=2/3>")
+        b.wait(3)
+        bunch.wait_for_finished()
+        self.assertRegex(repr(b), r"<\w+\.Barrier at .*: waiters=0/3>")
+        b.abort()
+        self.assertRegex(repr(b), r"<\w+\.Barrier at .*: broken>")

Lib/threading.py

@@ -418,6 +418,11 @@ class Semaphore:
         self._cond = Condition(Lock())
         self._value = value
 
+    def __repr__(self):
+        cls = self.__class__
+        return (f"<{cls.__module__}.{cls.__qualname__} at {id(self):#x}:"
+                f" value={self._value}>")
+
     def acquire(self, blocking=True, timeout=None):
         """Acquire a semaphore, decrementing the internal counter by one.
 
@@ -504,6 +509,11 @@ class BoundedSemaphore(Semaphore):
         Semaphore.__init__(self, value)
         self._initial_value = value
 
+    def __repr__(self):
+        cls = self.__class__
+        return (f"<{cls.__module__}.{cls.__qualname__} at {id(self):#x}:"
+                f" value={self._value}/{self._initial_value}>")
+
     def release(self, n=1):
         """Release a semaphore, incrementing the internal counter by one or more.
 
@@ -539,6 +549,11 @@ class Event:
         self._cond = Condition(Lock())
         self._flag = False
 
+    def __repr__(self):
+        cls = self.__class__
+        status = 'set' if self._flag else 'unset'
+        return f"<{cls.__module__}.{cls.__qualname__} at {id(self):#x}: {status}>"
+
     def _at_fork_reinit(self):
         # Private method called by Thread._reset_internal_locks()
         self._cond._at_fork_reinit()
@@ -637,6 +652,13 @@ class Barrier:
         self._state = 0 #0 filling, 1, draining, -1 resetting, -2 broken
         self._count = 0
 
+    def __repr__(self):
+        cls = self.__class__
+        if self.broken:
+            return f"<{cls.__module__}.{cls.__qualname__} at {id(self):#x}: broken>"
+        return (f"<{cls.__module__}.{cls.__qualname__} at {id(self):#x}:"
+                f" waiters={self.n_waiting}/{self.parties}>")
+
     def wait(self, timeout=None):
         """Wait for the barrier.
 

Misc/NEWS.d/next/Library/2020-05-30-10-48-04.bpo-24391.ZCTnhX.rst

@@ -0,0 +1,3 @@
+Improved reprs of :mod:`threading` synchronization objects:
+:class:`~threading.Semaphore`, :class:`~threading.BoundedSemaphore`,
+:class:`~threading.Event` and :class:`~threading.Barrier`.