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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 rt_time_log(logfile, startdate):
 """ Open and read reftek raw log-file. Function to open and read a log-file as written by a RefTek RT130 datalogger. The information within is then scanned for timing errors above the threshold. :type logfile: str :param logfile: The logfile to look in :type startdate: datetime.date :param startdate: The start of the file as a date - files contain timing \ and the julian day, but not the year. :returns: List of tuple of (:class:`datetime.datetime`, float) as time \ stamps and phase error. """

    if os.name == 'nt':
        f = io.open(logfile, 'rb')
    else:
        f = io.open(logfile, 'rb')
    phase_err = []
    lock = []
    # Extract all the phase errors
    for line_binary in f:
        try:
            line = line_binary.decode("utf8", "ignore")
        except UnicodeDecodeError:
            warnings.warn('Cannot decode line, skipping')
            continue
        if re.search("INTERNAL CLOCK PHASE ERROR", line):
            match = re.search("INTERNAL CLOCK PHASE ERROR", line)
            d_start = match.start() - 13
            phase_err.append((dt.datetime.strptime(str(startdate.year) +
                                                   ':' +
                                                   line[d_start:d_start + 12],
                                                   '%Y:%j:%H:%M:%S'),
                             float(line.rstrip().split()[-2]) *
                             0.000001))
        elif re.search("EXTERNAL CLOCK POWER IS TURNED OFF", line):
            match = re.search("EXTERNAL CLOCK POWER IS TURNED OFF", line)
            d_start = match.start() - 13
            lock.append((dt.datetime.strptime(str(startdate.year) +
                                              ':' + line[d_start:d_start + 12],
                                              '%Y:%j:%H:%M:%S'),
                        999))
    if len(phase_err) == 0 and len(lock) > 0:
        phase_err = lock
    f.close()
    return phase_err