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It is really nice to have the open/closed status in the __repr__ of file objects: 
 <open file 'data.txt', mode 'r' at 0x102c8ec90>
 <closed file 'data.txt', mode 'r' at 0x102c8ec90>
I would like to have the same for locks:
 <unlocked thread.lock object at 0x1002b1330>
 <locked thread.lock object at 0x1002b1330>
This would be nice in logs and tracebacks for example.

Here's a patch with a test. Example repr of threading.Lock():
 $ ./python -c "import threading; print(threading.Lock())"
 <unlocked _thread.lock object>

The repr of threading._RLock contains owner and count, but not lock/unlock status. The repr of locks from _dummy_thread also should contain lock/unlock status. And it would be nice to have the open/closed status in the repr of other synchronization primitives: Condition, Semaphore, etc. 
As for tests, I think assertRegex() will produce more useful error report.

And of course we should keep "at 0x..." part, because it is the way to distinguish different lock objects.

> The repr of threading._RLock contains owner and count, but not
> lock/unlock status. The repr of locks from _dummy_thread also should
> contain lock/unlock status. And it would be nice to have the
> open/closed status in the repr of other synchronization primitives:
> Condition, Semaphore, etc. 
I think it's ok to stay focussed and restrict this issue to threading.Lock (and perhaps RLock).
Berker, do you want to provide an updated patch?

Here's an updated patch. Thanks for the reviews.
> And of course we should keep "at 0x..." part, because it is the way to distinguish different lock objects.
Done.
 $ ./python -c "import threading; l = threading.Lock(); print(l)"
 <unlocked _thread.lock object at 0x7f0a19e7b1f8>
> The repr of threading._RLock contains owner and count, but not lock/unlock status.
Done.
 $ ./python -c "import threading; rl = threading.RLock(); rl.acquire(); print(rl)"
 <locked _thread.RLock object owner=139769600231168 count=1>
> The repr of locks from _dummy_thread also should contain lock/unlock status.
Done.
 $ ./python -c "import dummy_threading as threading; l = threading.Lock(); print(l)"
 <unlocked _dummy_thread.LockType object at 0x7fb334245400>
 $ ./python -c "import dummy_threading as threading; l = threading.RLock(); print(l)"
 <unlocked threading._RLock object owner=None count=0 at 0x7f524d0138e0>
> As for tests, I think assertRegex() will produce more useful error report.
Done.

The patch is just about ready to go but needs to address some failing tests:
======================================================================
FAIL: test_locked_repr (test.test_importlib.test_locks.Frozen_ModuleLockAsRLockTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/Users/raymond/cpython/Lib/test/lock_tests.py", line 91, in test_locked_repr
 self.assertRegex(repr(lock), "<locked .* object (.*)?at .*>")
AssertionError: Regex didn't match: '<locked .* object (.*)?at .*>' not found in "_ModuleLock('some_lock') at 4438138048"
======================================================================
FAIL: test_repr (test.test_importlib.test_locks.Frozen_ModuleLockAsRLockTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/Users/raymond/cpython/Lib/test/lock_tests.py", line 85, in test_repr
 self.assertRegex(repr(lock), "<unlocked .* object (.*)?at .*>")
AssertionError: Regex didn't match: '<unlocked .* object (.*)?at .*>' not found in "_ModuleLock('some_lock') at 4439151784"
======================================================================
FAIL: test_locked_repr (test.test_importlib.test_locks.Source_ModuleLockAsRLockTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/Users/raymond/cpython/Lib/test/lock_tests.py", line 91, in test_locked_repr
 self.assertRegex(repr(lock), "<locked .* object (.*)?at .*>")
AssertionError: Regex didn't match: '<locked .* object (.*)?at .*>' not found in "_ModuleLock('some_lock') at 4438192312"
======================================================================
FAIL: test_repr (test.test_importlib.test_locks.Source_ModuleLockAsRLockTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/Users/raymond/cpython/Lib/test/lock_tests.py", line 85, in test_repr
 self.assertRegex(repr(lock), "<unlocked .* object (.*)?at .*>")
AssertionError: Regex didn't match: '<unlocked .* object (.*)?at .*>' not found in "_ModuleLock('some_lock') at 4438192480"
----------------------------------------------------------------------
Ran 970 tests in 0.549s
FAILED (failures=4, skipped=7, expected failures=1)
test test_importlib failed
1 test failed:
 test_importlib

Here is a new patch. I've disabled test_repr and test_locked_repr tests in Lib/test/test_importlib/test_locks.py.

New changeset 7574f94b1068 by Raymond Hettinger in branch 'default':
Issue 21137: Better repr for threading.Lock()
http://hg.python.org/cpython/rev/7574f94b1068 

Thanks Berker.