title: ufunc 'add' did not contain loop with signature matching type dtype ('S32') ('S32') ('S32')
body: <p>I'm trying to run someone's script for some simulations I've made to try plotting some histograms, but when I do I always get the error message mentioned above. I have no idea what's gone wrong.</p>
  <p>Here's the complete traceback error I get:</p>
  <pre class="lang-none prettyprint-override"><code>File &quot;AVAnalyse.py&quot;, line 205, in &lt;module&gt; 
    f.write(line[0] + '  ' + line[1] + '  ' + line[2] + '  ' + line[3]) 
  TypeError: ufunc 'add' did not contain a loop with signature matching types dtype('S32') dtype('S32') dtype('S32')
  </code></pre>
  <p>This is the code I am trying to run:</p>
  <pre><code>name_out = &quot;histogram_&quot; + donor + &quot;_&quot; + acceptor + &quot;.dat&quot;   
  f = open(name_out, 'w')
  f.write('distance  d.probability  efficiency  e.probability')
  for line in dist_hist:
      f.write(line[0] + '  ' + line[1] + '  ' + line[2] + '  ' + line[3])
  f.close()
  
  print &quot;data saved in &quot; + &quot;histogram_&quot; + donor + &quot;_&quot; + acceptor + &quot;.dat&quot;
  </code></pre>
  <p>What am I doing wrong?</p>