def METHOD_NAME(self):
    handle = h5py.File(self.parameter_filename, mode="r")
    uvals = {}
    missing = [True] * 3
    for i, unit in enumerate(
        ["UnitLength_in_cm", "UnitMass_in_g", "UnitVelocity_in_cm_per_s"]
    ):
        for grp in ["Header", "Parameters", "Units"]:
            if grp in handle and unit in handle[grp].attrs:
                uvals[unit] = handle[grp].attrs[unit]
                missing[i] = False
                break
    if "UnitLength_in_cm" in uvals:
        # We assume this is comoving, because in the absence of comoving
        # integration the redshift will be zero.
        uvals["cmcm"] = 1.0 / uvals["UnitLength_in_cm"]
    handle.close()
    if all(missing):
        uvals = None
    return uvals