import yt

ds = yt.load(...)
ad = ds.all_data()
virial = ds.arr(1.4,'Mpc/h')
sph = ds.sphere([.5,.5,.5],5.*virial)
profile  = yt.ProfilePlot(sph,'radius',('gas','temperature'),x_log=False,weight_field='cell_mass')

rrvir = np.array(profile.profiles[0].x/virial)