title: align arrays with python
body: <p>I have 3 files (<code>file1.txt</code>, <code>file2.txt</code>, <code>file3.txt</code>) that look like:</p>
  
  <p>file1:</p>
  
  <pre><code>-7  12
  -6  13
  -5  11
  -4  10
  -3  4
  -2  8
  -1  7
  0   9
  1   10
  </code></pre>
  
  <p>file2:</p>
  
  <pre><code>-5  13
  -4  4
  -3  5
  -2  4
  -1  7
  0   6
  1   9
  2   10
  3   2
  </code></pre>
  
  <p>file3:</p>
  
  <pre><code>-2  3
  -1  14
  0   8
  1   7
  2   3
  3   9
  4   10
  5   8
  6   3
  </code></pre>
  
  <p>I want to align the zeros of the arrays I read from these files and get the sum of the values on the right, that is getting something like:</p>
  
  <pre><code>-7  -&gt;  12  + 0  + 0  =  12
  -6  -&gt;  13  + 0  + 0  =  13
  -5  -&gt;  11  + 13 + 0  =  24
  -4  -&gt;  10  + 4  + 0  =  14
  -3  -&gt;  4   + 5  + 0  =  9
  -2  -&gt;  8   + 4  + 3  =  15
  -1  -&gt;  7   + 7  + 14 =  28
  0   -&gt;  9   + 6  + 8  =  23
  1   -&gt;  10  + 9  + 7  =  26
  2   -&gt;  0   + 10 + 3  =  13
  3   -&gt;  0   + 2  + 9  =  11
  4   -&gt;  0   + 0  + 10 =  10
  5   -&gt;  0   + 0  + 8  =  8
  6   -&gt;  0   + 0  + 3  =  3
  7   -&gt;  0   + 0  + 0  =  0
  </code></pre>
  
  <p>How could I do that, with Python? Thank you in advance.</p>