title: Pandas: Sum of the Max 3 Column Values in Each Row
body: <p>Sample data:</p>
  
  <pre><code>        0        1         2        3       4  Sum_max_3
  0  591949  2575703  22479693  2202865  499835   27258261
  1    2705    11426    339913     5438    1016     356777
  2      18      119      4162       18       0       4299
  3     264     1213     14999      246     116      16476
  4       0       35      1292       10       0       1337
  5       0        0      1442        0       0       1442
  6       0       28      5596       20       0       5644
  7       0       10       102       56       0        168
  8      33        0      1224       17       0       1274
  9      39      198      9505       62      35       9765
  </code></pre>
  
  <p>I want to get the sum of the 3 columns with the largest values in the row. These are different columns for every row (Sum_max_3).</p>
  
  <p>I have many many columns so I need to do this automatically for all of them.</p>