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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 waitgrab(self, timeout=60, autocrop=True, cb_imgcheck=None):
        '''start process and create screenshot.
        Repeat screenshot until it is not empty and
        cb_imgcheck callback function returns True
        for current screenshot.

        :param autocrop: True -> crop screenshot
        :param timeout: int
        :param cb_imgcheck: None or callback for testing img,
                            True = accept img,
                            False = reject img
        '''
        t = 0
        sleep_time = 0.3  # for fast windows
        repeat_time = 1
        while 1:
            log.debug('sleeping %s secs' % str(sleep_time))
            time.sleep(sleep_time)
            t += sleep_time
            img = self.grab(autocrop=autocrop)
            if img:
                if not cb_imgcheck:
                    break
                if cb_imgcheck(img):
                    break
            sleep_time = repeat_time
            repeat_time += 1  # progressive
            if t > timeout:
                msg = 'Timeout! elapsed time:%s timeout:%s ' % (t, timeout)
                raise DisplayTimeoutError(msg)
                break

            log.debug('screenshot is empty, next try..')
        assert img
#        if not img:
#            log.debug('screenshot is empty!')
        return img