#NEWLINE# @ dispatch ( Broadcast ) #NEWLINE# def _lean( expr , fields = None ) : #NEWLINE# #INDENT# fields = ( set ( fields ) | set ( expr . active_columns ( ) ) ) #NEWLINE# ( child , _ ) = _lean ( expr . _child , fields = fields ) #NEWLINE# return ( expr . _subs ( { #NEWLINE# #INDENT# expr . _child : child , #NEWLINE# #UNINDENT# } ) , fields )