def join2sql_gen(value, table_is_esc=False):

    '''Converts old-style (tuple-based) joins to sql_gen-compatible values.

    @param table_is_esc If False, assumes any table name is not escaped or that

        re-escaping it will produce the same value.

    '''

    if isinstance(value, Join): return value # already in sql_gen form

    assert isinstance(value, tuple)

    table, joins = value

    return Join(table2sql_gen(table, table_is_esc), joins)