code: def parse_leap_seconds(fileobj):
      
      lines = iter(fileobj)
      for line in lines:
          if line.startswith(b'#  File expires on'):
              break
      else:
          raise ValueError('Leap_Second.dat is missing its expiration date')
      line = line.decode('ascii')
  
      with _lock:  # won't help if anyone user threads are doing parsing, alas
          original_locale = locale.setlocale(locale.LC_ALL)
          locale.setlocale(locale.LC_ALL, 'C')
          try:
              dt = datetime.strptime(line, '#  File expires on %d %B %Y\n')
          finally:
              locale.setlocale(locale.LC_ALL, original_locale)
  
      # The file went out of date at the beginning of July 2016, and kept
      # downloading every time a user ran a Skyfield program.  So we now
      # build in a grace period:
      grace_period = timedelta(days=30)
      expiration_date = dt.date() + grace_period
      mjd, day, month, year, offsets = np.loadtxt(lines).T
      leap_dates = np.ndarray(len(mjd) + 2)
      leap_dates[0] = '-inf'
      leap_dates[1:-1] = mjd + 2400000.5
      leap_dates[-1] = 'inf'
      leap_offsets = np.ndarray(len(mjd) + 2)
      leap_offsets[0] = leap_offsets[1] = offsets[0]
      leap_offsets[2:] = offsets
      return expiration_date, (leap_dates, leap_offsets)
docs: Parse the IERS file ``Leap_Second.dat``.
  
      The leap dates array can be searched with::
  
          index = np.searchsorted(leap_dates, jd, 'right')
  
      The resulting index allows (TAI - UTC) to be fetched with::
  
          offset = leap_offsets[index]