def METHOD_NAME(self, sub_file, pdtype=None, pshape=None):
    # We do not need the pdtype and the pshape, but some frontends do so we
    # accept them and then just ignore them
    ptype = self.ds._sph_ptypes[0]
    ind = int(ptype[-1])
    si, ei = sub_file.start, sub_file.end
    with h5py.File(sub_file.filename, mode="r") as f:
        pcount = f["/Header"].attrs["NumPart_ThisFile"][ind].astype("int")
        pcount = np.clip(pcount - si, 0, ei - si)
        # we upscale to float64
        hsml = f[ptype]["SmoothingLength"][si:ei, ...]
        hsml = hsml.astype("float64", copy=False)
        return hsml