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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 determine_alert(self, action_schedule, issue_creation_time, last_alert):
 """Determine if we need to trigger an alert Args: action_schedule (`list`):
 A list contains the alert schedule issue_creation_time (`int`):
 Time we create the issue last_alert (`str`):
 Time we sent the last alert Returns: (`None` or `str`) None if no alert should be sent. Otherwise return the alert we should send """

        issue_age = time.time() - issue_creation_time
        alert_schedule_lookup = {pytimeparse.parse(action_time): action_time for action_time in action_schedule}
        alert_schedule = sorted(alert_schedule_lookup.keys())
        last_alert_time = pytimeparse.parse(last_alert)

        for alert_time in alert_schedule:
            if last_alert_time < alert_time <= issue_age and last_alert_time != alert_time:
                return alert_schedule_lookup[alert_time]
        else:
            return None