How to use the h5pyd.Reference function in h5pyd

# scalar byte values
        g1.attrs['e1'] = "Hello"
        s = g1.attrs['e1']
        self.assertEqual(s, "Hello" )

        # scalar objref attribute
        g11 = g1.create_group('g1.1') # create subgroup g1/g1.1
        g11.attrs['name'] = 'g1.1'   # tag group with an attribute

        if is_hsds:
            # following is not working with h5serv
            g11_ref = g11.ref   # get ref to g1/g1.1
            self.assertTrue(isinstance(g11_ref, h5py.Reference))
            refdt = h5py.special_dtype(ref=h5py.Reference)  # create ref dtype
            g1.attrs.create('f1', g11_ref, dtype=refdt)     # create attribute with ref to g1.1
            ref = g1.attrs['f1'] # read back the attribute

            refobj = f[ref]  # get the ref'd object
            self.assertTrue('name' in refobj.attrs)  # should see the tag attribute
            self.assertEqual(refobj.attrs['name'], 'g1.1')  # check tag value


        # close file
        f.close()

# scalar byte values
        g1.attrs['e1'] = "Hello"
        s = g1.attrs['e1']
        self.assertEqual(s, "Hello" )

        # scalar objref attribute
        g11 = g1.create_group('g1.1') # create subgroup g1/g1.1
        g11.attrs['name'] = 'g1.1'   # tag group with an attribute

        if is_hsds:
            # following is not working with h5serv
            g11_ref = g11.ref   # get ref to g1/g1.1
            self.assertTrue(isinstance(g11_ref, h5py.Reference))
            refdt = h5py.special_dtype(ref=h5py.Reference)  # create ref dtype
            g1.attrs.create('f1', g11_ref, dtype=refdt)     # create attribute with ref to g1.1
            ref = g1.attrs['f1'] # read back the attribute

            refobj = f[ref]  # get the ref'd object
            self.assertTrue('name' in refobj.attrs)  # should see the tag attribute
            self.assertEqual(refobj.attrs['name'], 'g1.1')  # check tag value


        # close file
        f.close()

r = f['/']
        is_h5serv = False
        if isinstance(f.id.id, str) and not f.id.id.startswith("g-"):
            is_h5serv = True  # h5serv doesn't have support for objref datasets yet

        # create subgroup g1
        r.create_group('g1')
        self.assertTrue('g1' in r)
        g1 = r['g1']

        # create subgroup g1/g1.1
        g11 = g1.create_group('g1.1')

        # get ref to g1/g1.1
        g11_ref = g11.ref
        self.assertTrue(isinstance(g11_ref, h5py.Reference))
        self.assertEqual(g11.name, "/g1/g1.1")

        # create subgroup g2
        r.create_group('g2')
        self.assertEqual(len(r), 2)
        g2 = r['g2']

        # get ref to g1/g1.1 from g2
        g11ref = g2[g11_ref]

        # create subgroup /g1/g1.1/foo
        g11ref.create_group("foo")
        self.assertEqual(len(g11), 1)
        self.assertTrue("foo" in g11)

        # create datset /g2/d1

dtvlen = h5py.special_dtype(vlen=dtref)
        e0 = np.array((g1_1.ref,), dtype=dtref)
        e1 = np.array((g1_1.ref,g1_2.ref), dtype=dtref)
        e2 = np.array((g1_1.ref,g1_2.ref,g1_3.ref), dtype=dtref)
        data = [e0,e1,e2]

        g1.attrs.create("b1", data, shape=(3,),dtype=dtvlen)

        vlen_val = g1.attrs["b1"]  # read back attribute
        self.assertTrue(isinstance(vlen_val, np.ndarray))
        self.assertEqual(len(vlen_val), 3)
        for i in range(3):
            e = vlen_val[i]
            self.assertTrue(isinstance(e, np.ndarray))
            ref_type = h5py.check_dtype(ref=e.dtype)
            self.assertEqual(ref_type, h5py.Reference)
            # TBD - h5pyd is returning shape of () rather than (1,) for singletons
            if i>0:
                self.assertEqual(e.shape, ((i+1),))
                # first element is always a ref to g1
                refd_group = f[e[0]]
                self.assertEqual(refd_group.attrs['name'], 'g1_1')

        # create an attribute with compound type of vlen objref and int32
        dtcompound = np.dtype([('refs', dtvlen), ('number', 'int32')])
        # create np array with data for the attribute
        # note: two step process is needed, see: https://github.com/h5py/h5py/issues/573
        data = np.zeros((2,), dtype=dtcompound)
        data[0] = (e1, 1)
        data[1] = (e2, 2)

        g1.attrs.create("c1", data, shape=(2,), dtype=dtcompound)

ret_val = g1.attrs["a1"]
        self.assertTrue(isinstance(ret_val, np.ndarray))
        self.assertEqual(len(ret_val), 2)
        self.assertTrue(isinstance(ret_val[0], np.ndarray))
        # py36  attribute[a1]: [array([0, 1, 2], dtype=int32) array([0, 1, 2, 3], dtype=int32)]
        # py27  [(0, 1, 2) (0, 1, 2, 3)]
        self.assertEqual(list(ret_val[0]), [0,1,2])
        self.assertEqual(ret_val[0].dtype, np.dtype('int32'))
        self.assertTrue(isinstance(ret_val[1], np.ndarray))
        self.assertEqual(ret_val[1].dtype, np.dtype('int32'))

        self.assertEqual(list(ret_val[1]), [0,1,2,3])

        # create an attribute that is VLEN ObjRef
        dtref = h5py.special_dtype(ref=h5py.Reference)
        dtvlen = h5py.special_dtype(vlen=dtref)
        e0 = np.array((g1_1.ref,), dtype=dtref)
        e1 = np.array((g1_1.ref,g1_2.ref), dtype=dtref)
        e2 = np.array((g1_1.ref,g1_2.ref,g1_3.ref), dtype=dtref)
        data = [e0,e1,e2]

        g1.attrs.create("b1", data, shape=(3,),dtype=dtvlen)

        vlen_val = g1.attrs["b1"]  # read back attribute
        self.assertTrue(isinstance(vlen_val, np.ndarray))
        self.assertEqual(len(vlen_val), 3)
        for i in range(3):
            e = vlen_val[i]
            self.assertTrue(isinstance(e, np.ndarray))
            ref_type = h5py.check_dtype(ref=e.dtype)
            self.assertEqual(ref_type, h5py.Reference)

# get ref to d1
        d1_ref = d1.ref
        dt = h5py.special_dtype(ref=h5py.Reference)
        self.assertTrue(dt.metadata['ref'] is h5py.Reference)
        ref = h5py.check_dtype(ref=dt)
        self.assertEqual(ref, h5py.Reference)


        if is_h5serv:
            return  # ref types not supported in h5serv

        # create dataset of ref types
        dset = g1.create_dataset('myrefs', (10,), dtype=dt)
        ref = h5py.check_dtype(ref=dset.dtype)
        self.assertEqual(ref, h5py.Reference)

        dset[0] = g11_ref
        dset[1] = d1_ref

        a_ref = dset[0]
        obj = f[a_ref]
        if not config.get("use_h5py"):
            self.assertEqual(obj.id.id, g11.id.id)  # ref to g1.1
        self.assertEqual(obj.name, "/g1/g1.1")

        b_ref = dset[1]
        obj = f[b_ref]
        if not config.get("use_h5py"):
            self.assertEqual(obj.id.id, d1.id.id)  # ref to d1
        self.assertEqual(obj.name, "/g2/d1")

fields = []
        for name in srcdt.fields:
            item = srcdt.fields[name]
            # item is a tuple of dtype and integer offset
            field_dt = convert_dtype(item[0], ctx)
            fields.append((name, field_dt))
        tgt_dt = np.dtype(fields)
    else:
        # check if this a "special dtype"
        if srcdt.metadata and 'ref' in srcdt.metadata:
            ref = srcdt.metadata['ref']
            if is_reference(ref):
                if is_h5py(ctx['fout']):
                    tgt_dt = h5py.special_dtype(ref=h5py.Reference)
                else:
                    tgt_dt = h5pyd.special_dtype(ref=h5pyd.Reference)
            elif is_regionreference(ref):
                if is_h5py(ctx['fout']):
                    tgt_dt = h5py.special_dtype(ref=h5py.RegionReference)
                else:
                    tgt_dt = h5py.special_dtype(ref=h5py.RegionReference)
            else:
                msg = "Unexpected ref type: {}".format(srcdt)
                logging.error(msg)
                raise TypeError(msg)
        elif srcdt.metadata and 'vlen' in srcdt.metadata:
            src_vlen = srcdt.metadata['vlen']
            if isinstance(src_vlen, np.dtype):
                tgt_base = convert_dtype(src_vlen, ctx)
            else:
                tgt_base = src_vlen
            if is_h5py(ctx['fout']):