#NEWLINE# def keywords( self , fileids = None ) : #NEWLINE# #INDENT# '\n        Return a set of all keywords used in the corpus.\n\n        :param fileids: a list or regexp specifying the ids of the files whose\n            keywords have to be returned.\n        :return: the set of keywords and comparative phrases used in the corpus.\n        :rtype: set(str)\n        ' #NEWLINE# all_keywords = concat ( [ self . CorpusView ( path , self . _read_keyword_block , encoding = enc ) for ( path , enc , fileid ) in self . abspaths ( fileids , True , True ) ] ) #NEWLINE# keywords_set = set ( [ keyword . lower ( ) for keyword in all_keywords if keyword ] ) #NEWLINE# return keywords_set