How to use the plyfile.PlyProperty function in plyfile

def test_assign_properties_error(tet_ply_txt):
    vertex = tet_ply_txt['vertex']
    with Raises(ValueError) as e:
        vertex.properties = (vertex.properties +
                             (PlyProperty('xx', 'i4'),))
    assert str(e) == "dangling property 'xx'"

def test_element_parse_error_repr():
    prop = PlyProperty('x', 'f4')
    elt = PlyElement('test', [prop], 0)
    e = PlyElementParseError('text', elt, 0, prop)
    assert repr(e)

"{len_type} {val_type} {name}\"")

            try:
                properties.append(
                    PlyListProperty(fields[3], fields[1], fields[2])
                )
            except ValueError as e:
                self._error(str(e))

        else:
            if len(fields) != 2:
                self._error("expected \"property {type} {name}\"")

            try:
                properties.append(
                    PlyProperty(fields[1], fields[0])
                )
            except ValueError as e:
                self._error(str(e))

'''
        Write data to a binary stream.

        '''
        _write_array(stream, _np.dtype(self.dtype(byte_order)).type(data))

    def __str__(self):
        val_str = _data_type_reverse[self.val_dtype]
        return 'property %s %s' % (val_str, self.name)

    def __repr__(self):
        return 'PlyProperty(%r, %r)' % (self.name,
                                        _lookup_type(self.val_dtype))


class PlyListProperty(PlyProperty):

    '''
    PLY list property description.

    '''

    def __init__(self, name, len_dtype, val_dtype):
        PlyProperty.__init__(self, name, val_dtype)

        self.len_dtype = len_dtype

    def _get_len_dtype(self):
        return self._len_dtype

    def _set_len_dtype(self, len_dtype):
        self._len_dtype = _data_types[_lookup_type(len_dtype)]

if t[1][1] == 'O':
                    if len(t) != 2:
                        raise ValueError("non-scalar object fields not "
                                         "supported")

                len_str = _data_type_reverse[len_types.get(t[0], 'u1')]
                if t[1][1] == 'O':
                    val_type = val_types.get(t[0], 'i4')
                    val_str = _lookup_type(val_type)
                else:
                    val_str = _lookup_type(t[1][1:])

                prop = PlyListProperty(t[0], len_str, val_str)
            else:
                val_str = _lookup_type(t[1][1:])
                prop = PlyProperty(t[0], val_str)

            properties.append(prop)

        elt = PlyElement(name, properties, count, comments)
        elt.data = data

        return elt