Right after I sent the preceding message I got a funny feeling I'm wasting everybody's time here. I apologize. Guido's original concern about speedy C implementation for locks stands. I don't see a good way around it. By the way, my expansion of 'with' using coroutines (in previous message) was incorrect. The corrected version is shorter; see below. -j This: with EXPR as VAR: BLOCK would expand to this under PEP 342 and my proposal: _cm = (EXPR).__with__() VAR = _cm.next() try: BLOCK except: _cm.throw(*sys.exc_info()) finally: try: _cm.next() except (StopIteration, GeneratorExit): pass else: raise RuntimeError("coroutine didn't finish")