#NEWLINE# def default( self , field , value ) : #NEWLINE# #INDENT# '\n        \n        The ``default`` method sets the value of ``field`` to ``value``\n        only if the current value is ``None``. This way the method can be used to compact\n        initialize the value of a session field.\n        \n        ' #NEWLINE# if ( self [ field ] is None ) : #NEWLINE# #INDENT# self [ field ] = value