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I want to ask a question. In the producer-consumer with condition program, why there must be a two-layer while in the run() of consumer? I tried to write a consumer run() only with one while like this:
while True: self.condition.acquire( if len(self.integers) == 0: self.condition.wait() integer = self.integers.pop() print integer self.condition.release()
The program will crash for pop an empty list. For count of notify is same as the count of total integers appended to the list, before pop there must be at least one integer in the list, why wait() will return without a notify?

The blog post at http://www.laurentluce.com/posts/python-threads-synchronization-locks-rlocks-semaphores-conditions-events-and-queues/ is often quoted, for example from stack overflow answers.
However, the producer/consumer example using events is flawed and might make people implement this common pattern in a wrong way. The problem is as follows:

It's possible that the producer calls event.set() and event.clear() while the consumer is still processing the last integer and thus is not currently waiting for the event. By the time the consumer calls event.wait() again, the producer's call to event.clear() may have already completed and the consumer will then wait when it shouldn't, given that there's now an integer ready to be processed. Running the example code as-is multiple times shows this problem: the "xx popped from list" line is sometimes not printed 10 times as it should.

Given that this blog post has quite some exposure, it would make sense to fix this.