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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 mjd_obsc(self):
 """Given a CFHT Megaprime image header compute the center of exposure. This routine uses the calibration provide by Richard Wainscoat: From: Richard Wainscoat <rjw@ifa.hawaii.edu> Subject: Fwd: timing for MegaCam Date: April 24, 2015 at 7:23:09 PM EDT To: David Tholen <tholen@ifa.hawaii.edu> Looks like the midpoint of the exposure is now UTCEND - 0.73 sec - (exposure time / 2 ) Wobble on the 0.73 sec is +/- 0.15 sec. @rtype : float """

        # TODO Check if this exposure was taken afer or before correction needed.

        try:
            utc_end = self['UTCEND']
            exposure_time = float(self['EXPTIME'])
            date_obs = self['DATE-OBS']
        except KeyError as ke:
            raise KeyError("Header missing keyword: {}, required for MJD-OBSC computation".format(ke.args[0]))

        utc_end = Time(date_obs + "T" + utc_end)
        utc_cen = utc_end - TimeDelta(0.73, format='sec') - TimeDelta(exposure_time / 2.0, format='sec')
        return round(utc_cen.mjd, 7)