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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def check_future(self, fut):
 """Call with each future that is to be yielded on"""

        done = self.done = fut.done()
        if done and not self.prev_done:
            self.done_since = self.ioloop.time()
        self.prev_done = done