How to use the tractor.galaxy.ExpGalaxy function in tractor

sources.append(
                DevGalaxy(
                    PixPos(pos_x, pos_y), Flux(obj['flux']),
                    GalaxyShape(obj['a_arcsec'], (obj['b_arcsec'] / obj['a_arcsec']),
                                (90.0 + obj['theta'] * 180.0 / np.pi))))
        for obj in exp_galaxy:
            pos_x, pos_y = obj['x'], obj['y']
            sources.append(
                ExpGalaxy(
                    PixPos(pos_x, pos_y), Flux(obj['flux']),
                    GalaxyShape(obj['a_arcsec'], (obj['b_arcsec'] / obj['a_arcsec']),
                                (90.0 + obj['theta'] * 180.0 / np.pi))))
        for obj in rex_galaxy:
            pos_x, pos_y = obj['x'], obj['y']
            sources.append(
                ExpGalaxy(
                    PixPos(pos_x, pos_y), Flux(obj['flux']),
                    GalaxyShape(obj['a_arcsec'], (obj['b_arcsec'] / obj['a_arcsec']),
                                (90.0 + obj['theta'] * 180.0 / np.pi))))
        for obj in psf_galaxy:
            pos_x, pos_y = obj['x'], obj['y']
            sources.append(PointSource(PixPos(pos_x, pos_y), Flux(obj['flux'])))

        print("Now you have %d sources" % len(sources))

    elif shape_method is 'decals':
        ## Using DECaLS shapes
        if sources is None:
            sources = []
        for obj in comp_galaxy:
            pos_x, pos_y = obj['x'], obj['y']
            sources.append(

print('Creating Tractor catalog...')
    cat = []
    for i, t in enumerate(T):
        pos = RaDecPos(t.ra, t.dec)
        flux = NanoMaggies(**{wanyband: 1.})
        if all_ptsrcs:
            cat.append(PointSource(pos, flux))
            continue

        tt = t.type.strip()
        if tt in ['PTSRC', 'STAR', 'S']:
            cat.append(PointSource(pos, flux))
        elif tt in ['EXP', 'E']:
            shape = EllipseE(*t.shapeexp)
            cat.append(ExpGalaxy(pos, flux, shape))
        elif tt in ['DEV', 'D']:
            shape = EllipseE(*t.shapedev)
            cat.append(DevGalaxy(pos, flux, shape))
        elif tt in ['COMP', 'C']:
            eshape = EllipseE(*t.shapeexp)
            dshape = EllipseE(*t.shapedev)
            cat.append(FixedCompositeGalaxy(pos, flux, t.fracdev,
                                            eshape, dshape))
        else:
            print('Did not understand row', i, 'of input catalog:')
            t.about()
            assert(False)

    W = unwise_forcedphot(cat, tiles, roiradecbox=roiradecbox,
                          bands=opt.bands, unwise_dir=opt.unwise_dir,
                          use_ceres=opt.ceres, ceres_block=opt.ceresblock,

def _getModelPatches(self, img, minsb=0., modelMask=None):
        e = ExpGalaxy(self.pos, self.brightnessExp, self.shapeExp)
        d = DevGalaxy(self.pos, self.brightnessDev, self.shapeDev)
        if minsb == 0. or minsb is None:
            kw = {}
        else:
            kw = dict(minsb=minsb / 2.)
        if hasattr(self, 'halfsize'):
            e.halfsize = d.halfsize = self.halfsize
        pe = e.getModelPatch(img, modelMask=modelMask, **kw)
        pd = d.getModelPatch(img, modelMask=modelMask, **kw)
        return (pe, pd)

def switch_to_soft_ellipses(cat):
    from tractor.galaxy import DevGalaxy, ExpGalaxy, FixedCompositeGalaxy
    from tractor.ellipses import EllipseESoft
    for src in cat:
        if isinstance(src, (DevGalaxy, ExpGalaxy)):
            src.shape = EllipseESoft.fromEllipseE(src.shape)
        elif isinstance(src, FixedCompositeGalaxy):
            src.shapeDev = EllipseESoft.fromEllipseE(src.shapeDev)
            src.shapeExp = EllipseESoft.fromEllipseE(src.shapeExp)

def getProfile(self):
        return ExpGalaxy.profile

def __init__(self, *args, **kwargs):
        self.nre = ExpGalaxy.nre
        super(ExpGalaxy, self).__init__(*args, **kwargs)

def getParamDerivatives(self, img, modelMask=None):
        e = ExpGalaxy(self.pos, self.brightness, self.shapeExp)
        d = DevGalaxy(self.pos, self.brightness, self.shapeDev)
        e.dname = 'fcomp.exp'
        d.dname = 'fcomp.dev'

        if self.isParamFrozen('pos'):
            e.freezeParam('pos')
            d.freezeParam('pos')
        if self.isParamFrozen('shapeExp'):
            e.freezeParam('shape')
        if self.isParamFrozen('shapeDev'):
            d.freezeParam('shape')

        if hasattr(self, 'halfsize'):
            e.halfsize = self.halfsize
            d.halfsize = self.halfsize

def getParamDerivatives(self, img, modelMask=None):
        e = ExpGalaxy(self.pos, self.brightnessExp, self.shapeExp)
        d = DevGalaxy(self.pos, self.brightnessDev, self.shapeDev)
        if hasattr(self, 'halfsize'):
            e.halfsize = d.halfsize = self.halfsize
        e.dname = 'comp.exp'
        d.dname = 'comp.dev'
        if self.isParamFrozen('pos'):
            e.freezeParam('pos')
            d.freezeParam('pos')
        if self.isParamFrozen('brightnessExp'):
            e.freezeParam('brightness')
        if self.isParamFrozen('shapeExp'):
            e.freezeParam('shape')
        if self.isParamFrozen('brightnessDev'):
            d.freezeParam('brightness')
        if self.isParamFrozen('shapeDev'):
            d.freezeParam('shape')