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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(date_time):
 """Returns POSIX timestamp as float"""

    if date_time.tzinfo is None:
      return time.mktime((date_time.year, date_time.month, date_time.day, date_time.hour,
                          date_time.minute, date_time.second,
                          -1, -1, -1)) + date_time.microsecond / 1e6
    return (date_time - _EPOCH).total_seconds()