'Reads and returns the topics tree.
This auxiliary function reads and returns the topics tree file
contents for the CHM archive.'

def GetTopicsTree(self):

    if (self.topics is None):
        return None
    if self.topics:
        (res, ui) = chmlib.chm_resolve_object(self.file, self.topics)
        if (res != chmlib.CHM_RESOLVE_SUCCESS):
            return None
    (size, text) = chmlib.chm_retrieve_object(self.file, ui, 0L, ui.length)
    if (size == 0):
        sys.stderr.write('GetTopicsTree:    file    size    =    0\n')
        return None
    return text
