How to use the tractor.sdss.Tractor function in tractor

if s is None:
            continue
        if scale > 1:
            for im in ims:
                timgs.append(st.scale_sdss_image(im,scale))
        else:
            timgs.extend(ims)
        allsources.extend(s)
        sources.append(s)

    #rds = [rcf[3:5] for rcf in rcfs]
    #plotarea(ra, dec, fieldradius, name, prefix, timgs) #, rds)
    
    #lvl = logging.DEBUG
    #logging.basicConfig(level=lvl,format='%(message)s',stream=sys.stdout)
    tractor = st.Tractor(timgs, allsources, mp=mp)

    sa = dict(debug=True, plotAll=False,plotBands=False)

    if noarcsinh:
        sa.update(nlscale=0)
    elif dr8 or dr9:
        sa.update(chilo=-8.,chihi=8.)

    if nocache:
        tractor.cache = NullCache()
        sg.disable_galaxy_cache()

    zr = timgs[0].zr
    print "zr is: ",zr

    print bands

if s is None:
            continue
        if scale > 1:
            for im in ims:
                timgs.append(st.scale_sdss_image(im,scale))
        else:
            timgs.extend(ims)
        allsources.extend(s)
        sources.append(s)

    #rds = [rcf[3:5] for rcf in rcfs]
    #plotarea(ra, dec, fieldradius, name, prefix, timgs) #, rds)
    
    #lvl = logging.DEBUG
    #logging.basicConfig(level=lvl,format='%(message)s',stream=sys.stdout)
    tractor = st.Tractor(timgs, allsources, mp=mp)

    sa = dict(debug=True, plotAll=False,plotBands=False)

    if noarcsinh:
        sa.update(nlscale=0)
    elif dr8 or dr9:
        sa.update(chilo=-8.,chihi=8.)

    if nocache:
        tractor.cache = NullCache()
        sg.disable_galaxy_cache()

    zr = timgs[0].zr
    print("zr is: ",zr)

    print(bands)

allsources = []
    for ims,s in imsrcs:
        if ims is None:
            continue
        if s is None:
            continue
        timgs.extend(ims)
        allsources.extend(s)
        sources.append(s)

    #rds = [rcf[3:5] for rcf in rcfs]
    plotarea(ra, dec, radius, ngc, timgs) #, rds)
    
    lvl = logging.DEBUG
    logging.basicConfig(level=lvl,format='%(message)s',stream=sys.stdout)
    tractor = st.Tractor(timgs, allsources, mp=mp)

    sa = dict(debug=True, plotAll=False,plotBands=False)

    if noarcsinh:
        sa.update(nlscale=0)
    elif dr8:
        sa.update(chilo=-8.,chihi=8.)

    if opt.nocache:
        tractor.cache = NullCache()
        sg.disable_galaxy_cache()

    zr = timgs[0].zr
    print("zr is: ",zr)

    print(bands)

if s is None:
            continue
        if scale > 1:
            for im in ims:
                timgs.append(st.scale_sdss_image(im,scale))
        else:
            timgs.extend(ims)
        allsources.extend(s)
        sources.append(s)

    #rds = [rcf[3:5] for rcf in rcfs]
    #plotarea(ra, dec, fieldradius, name, prefix, timgs) #, rds)
    
    #lvl = logging.DEBUG
    #logging.basicConfig(level=lvl,format='%(message)s',stream=sys.stdout)
    tractor = st.Tractor(timgs, allsources, mp=mp)

    sa = dict(debug=True, plotAll=False,plotBands=False)

    if noarcsinh:
        sa.update(nlscale=0)
    elif dr8 or dr9:
        sa.update(chilo=-8.,chihi=8.)

    if nocache:
        tractor.cache = NullCache()
        sg.disable_galaxy_cache()

    zr = timgs[0].zr
    print("zr is: ",zr)

    print(bands)