def _get_version_for_class_from_state(state, klass):
        """ retrieves the version of the current klass from the state mapping from old locations to new ones. """
        # klass may have been renamed, so we have to look this up in the class rename registry.
        names = [_importable_name(klass)]
        # lookup old names, handled by current klass.
        from .util import class_rename_registry
        names.extend(class_rename_registry.old_handled_by(klass))
        for n in names:
            try:
                return state['class_tree_versions'][n]
            except KeyError:
                continue
        # if we did not find a suitable version number return infinity.
        if _debug:
            logger.debug('unable to obtain a __serialize_version for class %s', klass)
        return float('inf')
retrieves the version of the current klass from the state mapping from old locations to new ones.