title: Pandas: read file with special characters in a column
body: <p>In the data that I have, some feature values are <code>?</code>. How do I replace them with <code>NA</code>? </p>
  
  <p><strong>EDIT</strong></p>
  
  <p>The code and output is as below:</p>
  
  <pre><code>df = pd.read_csv("cca-census-income.csv", header = None)
  
  df.replace('?', np.nan, inplace=True)
  
  df.ix[0,]
  
  23                Other relative of householder
  24                                      1700.09
  25                                            ?
  26                                            ?
  27                                            ?
  28             Not in universe under 1 year old
  29                                            ?
  30                                            0
  </code></pre>