#NEWLINE# def __init__( self , table_name , field ) : #NEWLINE# #INDENT# 'Initialize an unbox expression.\n\n        :param table_name: The name of a table (a string).\n        :param field: An optional column name/index within the relation.\n        If None, the system uses index 0.\n        ' #NEWLINE# DottedRef . __init__ ( self , field , ( field or 0 ) ) #NEWLINE# self . table_name = table_name