title: pandas read_csv and setting na_values to any string in the csv file
body: <blockquote>
  <p>data.csv</p>
  <p>1, 22, 3432</p>
  <p>1, 23, \N</p>
  <p>2, 24, 54335</p>
  <p>2, 25, 3928</p>
  </blockquote>
  <p>I have a csv file of data that is collected from a device. Every now and then the device doesn't relay information and outputs '\N'. I want to treat these as NaN and did this by doing</p>
  <pre><code>read_csv(data.csv, na_values=['\\N']) 
  </code></pre>
  <p>which worked fine. However, I would prefer to have not only this string turned to NaN but any string that is in the csv file just in case the data I get in the future has a different string.</p>
  <p>Is it possible to me to make any changes in the argument so it covers all strings?</p>