python基礎練習---3*3マトリクスの主な対角線要素の和を求める

テーマ:ひとつの3*3行列の主な対角線の要素の和を求めます.
 
 

  1 # -*- coding:utf-8 -*-
  2 
  3 l1 = [[1, 1, 1], [2, 2, 2], [3, 3, 3]]
  4 for i in l1:
  5     print i
  6 num = 0
  7 for i in range(3):
  8     for j in range(3):
  9         a = l1[i]
 10         b = a[j]
 11         print b,
 12         if i == j:
 13             num += b
 14 print '      %d'%num

結果:
 

cl@cl-M14xR2:~/pythoncl/python  100 $ python 47.py 
[1, 1, 1]
[2, 2, 2]
[3, 3, 3]
1 1 1 2 2 2 3 3 3       6