On Tuesday, September 9, 2014 11:25:29 AM UTC+5:30, JBB wrote: > I have a list with a fixed number of elements which I need to grow; ie. add > rows of a fixed number of elements, some of which will be blank.
> e.g. [['a','b','c','d'], ['A','B','C','D'], ['', 'aa', 'inky', ''], ['', > 'bb', 'binky', ''], ... ] > This is a reduced representation of a larger list-of-lists problem that had > me running in circles today. > I think I figured out _how_ to get what I want but I am looking to > understand why one approach works and another doesn't. > 1) What does NOT work as desired: > proc_file = [] > proc_file = [['a','b','c','d']] > proc_file.append(['A','B','C','D']) > blank_r = ['','','',''] > qq = ['aa','bb','cc','dd'] > rr = ['inky', 'binky', 'pinky', 'clyde'] > for i,j in enumerate(zip(qq,rr)): > proc_file.append((blank_r)) # Add a row of blanks > proc_file[i+2][1] = j[0] > proc_file[i+2][2] = j[1] > print len(proc_file), blank_r, proc_file > print > print > proc_file > 3 ['', 'aa', 'inky', ''] [['a', 'b', 'c', 'd'], ['A', 'B', 'C', 'D'], ['', > 'aa', 'inky', '']] > 4 ['', 'bb', 'binky', ''] [['a', 'b', 'c', 'd'], ['A', 'B', 'C', 'D'], ['', > 'bb', 'binky', ''], ['', 'bb', 'binky', '']] > 5 ['', 'cc', 'pinky', ''] [['a', 'b', 'c', 'd'], ['A', 'B', 'C', 'D'], ['', > 'cc', 'pinky', ''], ['', 'cc', 'pinky', ''], ['', 'cc', 'pinky', '']] > 6 ['', 'dd', 'clyde', ''] [['a', 'b', 'c', 'd'], ['A', 'B', 'C', 'D'], ['', > 'dd', 'clyde', ''], ['', 'dd', 'clyde', ''], ['', 'dd', 'clyde', ''], ['', > 'dd', 'clyde', '']] > Out[82]: > [['a', 'b', 'c', 'd'], > ['A', 'B', 'C', 'D'], > ['', 'dd', 'clyde', ''], > ['', 'dd', 'clyde', ''], > ['', 'dd', 'clyde', ''], > ['', 'dd', 'clyde', '']] > 2) What works as desired: > proc_file = [] > proc_file = [['a','b','c','d']] > proc_file.append(['A','B','C','D']) > blank_r = ['','','',''] > qq = ['aa','bb','cc','dd'] > rr = ['inky', 'binky', 'pinky', 'clyde'] > for i,j in enumerate(zip(qq,rr)): > proc_file.append(list(blank_r)) # Change it to list(blank_r) and it works > proc_file[i+2][1] = j[0] > proc_file[i+2][2] = j[1] > print len(proc_file), blank_r, proc_file > print > print > proc_file > 3 ['', '', '', ''] [['a', 'b', 'c', 'd'], ['A', 'B', 'C', 'D'], ['', 'aa', > 'inky', '']] > 4 ['', '', '', ''] [['a', 'b', 'c', 'd'], ['A', 'B', 'C', 'D'], ['', 'aa', > 'inky', ''], ['', 'bb', 'binky', '']] > 5 ['', '', '', ''] [['a', 'b', 'c', 'd'], ['A', 'B', 'C', 'D'], ['', 'aa', > 'inky', ''], ['', 'bb', 'binky', ''], ['', 'cc', 'pinky', '']] > 6 ['', '', '', ''] [['a', 'b', 'c', 'd'], ['A', 'B', 'C', 'D'], ['', 'aa', > 'inky', ''], ['', 'bb', 'binky', ''], ['', 'cc', 'pinky', ''], ['', 'dd', > 'clyde', '']] > Out[83]: > [['a', 'b', 'c', 'd'], > ['A', 'B', 'C', 'D'], > ['', 'aa', 'inky', ''], > ['', 'bb', 'binky', ''], > ['', 'cc', 'pinky', ''], > ['', 'dd', 'clyde', '']] Dont quite know what you are trying to do. Does this serve your purpose? >>> proc_file = [['a','b','c','d']] >>> proc_file.append(['A','B','C','D']) >>> blank_r = ['','','',''] >>> [[i,j0,j1, ""] for (i, (j0, j1)) in enumerate(zip(qq,rr))] [[0, 'aa', 'inky', ''], [1, 'bb', 'binky', ''], [2, 'cc', 'pinky', ''], [3, 'dd', 'clyde', '']] Or if you prefer: >>> proc_file + [[i,j0,j1, ""] for (i, (j0, j1)) in enumerate(zip(qq,rr))] [['a', 'b', 'c', 'd'], [0, 'aa', 'inky', ''], [1, 'bb', 'binky', ''], [2, 'cc', 'pinky', ''], [3, 'dd', 'clyde', '']] -- https://mail.python.org/mailman/listinfo/python-list
