<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def sync(self, expectedThreads=0):
        'Wait for all but expectedThreads async threads to finish.'
        while len(self.unfinishedThreads) > expectedThreads:
            time.sleep(.3)
            self.checkForFinishedThreads()