def append(self, v):
        '''
        >>> d = DiskVarArray('/tmp/test3', dtype='uint32')
        >>> d.append([1, 2, 3, 4])
        >>> d.__getitem__(0)
        memmap([1, 2, 3, 4], dtype=uint32)
        >>> d.append([5, 6, 7, 8])
        >>> d.__getitem__(1)
        memmap([5, 6, 7, 8], dtype=uint32)
        >>> shutil.rmtree('/tmp/test3', ignore_errors=True)
        '''
        self.index.append(len(self.data))
        self.data.extend(v)
>>> d = DiskVarArray('/tmp/test3', dtype='uint32')
        >>> d.append([1, 2, 3, 4])
        >>> d.__getitem__(0)
        memmap([1, 2, 3, 4], dtype=uint32)
        >>> d.append([5, 6, 7, 8])
        >>> d.__getitem__(1)
        memmap([5, 6, 7, 8], dtype=uint32)
        >>> shutil.rmtree('/tmp/test3', ignore_errors=True)