import itertools list [[ , , ][ , , ][ ][ , ]merged list(itertools chain(*list )merged out[ ][[ ][ ][ ][ ]which one to choose in order to add elements efficientlylist comprehension old-fashioned way in [ ]my_list [for in range( )my_list append(imy_list out[ ][ one-line list comprehension in [ ]abs( () - out[ ]true in [ ]my_list [ /( + for in range( )my_list out[ ][ in [ ]my_list [ for in range( if my_list out[ ][ generator comprehension