Writing contour levels inline for each line

[neuronphysics]

I am trying to overlay contours on an image but I would like to use clabel and put some inline scales on the image but I wasn't successful and I couldn't find anything useful in the documentation of Aplpy
What I have written so far is like this :
def get_contour_verts(cn):
contours = []
# for each contour line
for cc in cn.collections:
paths = []
# for each separate section of the contour line
for pp in cc.get_paths():
xy = []
# for each segment of that section
for vv in pp.iter_segments():
xy.append(vv[0])
paths.append(np.vstack(xy))
contours.append(paths)
return contours

lev_exp = np.arange(np.floor(np.log10(zp.min())-1), np.ceil(np.log10(zp.max())+1))
levs = np.power(10, lev_exp)
bins_x=np.linspace(min(xp),max(xp),nx)
bins_y=np.linspace(min(yp),max(yp),ny)
H, yedges, xedges = np.histogram2d(xp, yp, (bins_x,bins_y),weights=zp)
smooth=0.7
Hsmooth = scipy.ndimage.filters.gaussian_filter(H.T, smooth)
xcenters = (xedges[1:] + xedges[:-1])/2.
ycenters = (yedges[1:] + yedges[:-1])/2.
Xgrid, Ygrid = np.meshgrid(ycenters, xcenters)
extent = [xedges[0], xedges[-1], yedges[0], yedges[-1] ]
print len(ra),len(Gcl_1_ra),len(Gcl_2_ra)

Now we add contours

CS = plt.contour(Xgrid, Ygrid, Hsmooth, levels=levs,extent=extent,norm=LogNorm())
Contour_arrays=get_contour_verts(CS)
for contours_at_level,c in zip(Contour_arrays,colors):
clines = [cl.T for cl in contours_at_level]
img.show_lines(clines[3:],color='white',layer='contour_set_1',linestyle='solid', linewidth=0.15, zorder=100)
img._layers['contour_set_1'].clabel(clines[3:], inline=1, fontsize=20., fmt=ticker.LogFormatterMathtext())
img.save('image_rgb_arcsinh_contour.pdf')
The error:
  File "Plot.Contour.Red.Galaxies.py", line 237, in
    img._layers['contour_set_1'].clabel(clines[3:], inline=1, fontsize=20., fmt=ticker.Log
FormatterMathtext())
AttributeError: 'LineCollection' object has no attribute 'clabel'
Is it possible to write the contour level over each line?