title: Python string formatting too slow
body: <p>I use the following code to log a map, it is fast when it only contains zeroes, but as soon as there is actual data in the map it becomes unbearably slow... Is there any way to do this faster?</p>
  
  <pre><code>log_file = open('testfile', 'w')
  for i, x in ((i, start + i * interval) for i in range(length)):
      log_file.write('%-5d %8.3f %13g %13g %13g %13g %13g %13g\n' % (i, x,
          map[0][i], map[1][i], map[2][i], map[3][i], map[4][i], map[5][i]))
  </code></pre>