#NEWLINE# def __getitem__( self , dim ) : #NEWLINE# #INDENT# "Get the columns selected for the given dimension name.\n\n        e.g. dim='x'\n\n        Returns:\n            the columns selected as a str or list(str). If the dimension is not in\n            `_selections`, `None` is returned.\n\n        " #NEWLINE# if ( dim in self . _selections ) : #NEWLINE# #INDENT# return self . _selections [ dim ] #NEWLINE# #UNINDENT# else : #NEWLINE# #INDENT# return None