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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 timestamp_from_datetime(dt):
 """ Given a datetime, in UTC, return a float that represents the timestamp for that datetime. http://stackoverflow.com/questions/8777753/converting-datetime-date-to-utc-timestamp-in-python#8778548 """

    dt = dt.replace(tzinfo=utc)
    if hasattr(dt, "timestamp") and callable(dt.timestamp):
        return dt.replace(tzinfo=utc).timestamp()
    return (dt - datetime(1970, 1, 1, tzinfo=utc)).total_seconds()