import yt

fname = 'GadgetDiskGalaxy/snapshot_200.hdf5'

unit_base = {'UnitLength_in_cm'         : 3.08568e+21,
             'UnitMass_in_g'            :   1.989e+43,
             'UnitVelocity_in_cm_per_s' :      100000}

bbox_lim = 1e5 #kpc

bbox = [[-bbox_lim,bbox_lim],
        [-bbox_lim,bbox_lim],
        [-bbox_lim,bbox_lim]]

ds = yt.load(fname,unit_base=unit_base,bounding_box=bbox)