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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 from_source_reference(expnum, ccd, x, y):
 """ Given the location of a source in the image, create an Observation. """


        image_uri = storage.dbimages_uri(expnum=expnum,
                                         ccd=None,
                                         version='p',
                                         ext='.fits',
                                         subdir=None)
        logger.debug('Trying to access {}'.format(image_uri))

        if not storage.exists(image_uri, force=False):
            logger.warning('Image not in dbimages? Trying subdir.')
            image_uri = storage.dbimages_uri(expnum=expnum,
                                             ccd=ccd,
                                             version='p')

        if not storage.exists(image_uri, force=False):
            logger.warning("Image doesn't exist in ccd subdir. %s" % image_uri)
            return None

        if x == -9999 or y == -9999:
            logger.warning("Skipping {} as x/y not resolved.".format(image_uri))
            return None

        mopheader_uri = storage.dbimages_uri(expnum=expnum,
                                             ccd=ccd,
                                             version='p',
                                             ext='.mopheader')
        if not storage.exists(mopheader_uri, force=False):
            # ELEVATE! we need to know to go off and reprocess/include this image.
            logger.critical('Image exists but processing incomplete. Mopheader missing. {}'.format(image_uri))
            return None

        # Build astrom.Observation
        observation = Observation(expnum=str(expnum),
                                  ftype='p',
                                  ccdnum=str(ccd),
                                  fk="")

        # JJK commented this out, I think the following line is not true?
        # observation.rawname = os.path.splitext(os.path.basename(image_uri))[0]+str(ccd).zfill(2)

        return observation