title: reading file with missing values in python pandas
body: <p>I try to read .txt with missing values using pandas.read_csv. My data is of the format:</p>
  
  <pre><code>10/08/2012,12:10:10,name1,0.81,4.02,50;18.5701400N,4;07.7693770E,7.92,10.50,0.0106,4.30,0.0301
  10/08/2012,12:10:11,name2,,,,,10.87,1.40,0.0099,9.70,0.0686
  </code></pre>
  
  <p>with thousands of samples with same name of the point, gps position, and other readings. 
  I use a code:</p>
  
  <pre><code>myData = read_csv('~/data.txt', sep=',', na_values='')
  </code></pre>
  
  <p>The code is wrong as na_values does not gives NaN or other indicator. Columns should have the same size but I finish with different length.</p>
  
  <p>I don't know what exactly should be typed in after na_values (did try all different things).
  Thanks </p>