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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 build_source_reading(expnum, ccd=None, ftype='p'):
 """ Build an astrom.Observation object for a SourceReading :param expnum: (str) Name or CFHT Exposure number of the observation. :param ccd: (str) CCD is this observation associated with. (can be None) :param ftype: (str) exposure time (specific to CFHT imaging) :return: An astrom.Observation object for the observation. :rtype: astrom.Observation """


        logger.debug("Building source reading for expnum:{} ccd:{} ftype:{}".format(expnum, ccd, ftype))

        return astrom.Observation(expnum=str(expnum),
                                  ftype=ftype,
                                  ccdnum=ccd)