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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 _decodeTimestamp(byteIter):
 """ Decodes a 7-octet timestamp """

    dateStr = decodeSemiOctets(byteIter, 7)
    timeZoneStr = dateStr[-2:]        
    return datetime.strptime(dateStr[:-2], '%y%m%d%H%M%S').replace(tzinfo=SmsPduTzInfo(timeZoneStr))