title: Pandas read_csv add header names in case of changing number of columns
body: <p>I have a lot of csv files that I would like to read with Pandas (pd.read_csv), however, in some of the files there is added a column midway that does not have a header, like this example:</p>
  
  <pre><code>Apples, Pears
  1, 2
  3, 4
  5, 6, 7
  </code></pre>
  
  <p>If using pd.read_csv(example_file) the following error is thrown "<em>ParserError: Error tokenizing data. C error: Expected 2 fields in line 4, saw 3</em>"</p>
  
  <p>I would like to avoid having to skip the line and instead just add a dummy header name, like Unknown1, and get the following result:</p>
  
  <pre><code>Apples, Pears, Unknown1  
  1, 2, np.nan
  3, 4, np.nan
  5, 6, 7
  </code></pre>