title: How to convert non-numeric entries to NaN in read_csv
body: <p>I am reading in a file with:</p>
  <pre><code>pd.read_csv(&quot;file.csv&quot;, dtype={'ID_1':float})
  </code></pre>
  <p>The file looks like:</p>
  <pre><code>ID_0, ID_1,ID_2
  a,002,c
  b,004,d
  c,   ,e       
  n,003,g
  </code></pre>
  <p>Unfortunately <code>read_csv</code> fails complaining it can't convert '  ' to a float.</p>
  <p>What is the right way to read in a csv and convert anything that can't be converted to a float into NaN?</p>