docs: 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)