title: Pandas Dataframe interpreting columns as float instead of String
body: <p>I want to import a csv file into a pandas dataframe. There is a column with IDs, which consist of only numbers, but not every row has an ID.</p>
  
  <pre><code>   ID      xyz
  0  12345     4.56
  1           45.60
  2  54231   987.00
  </code></pre>
  
  <p>I want to read this column as String, but even if I specifiy it with </p>
  
  <p><code>df=pd.read_csv(filename,dtype={'ID': str})</code></p>
  
  <p>I get </p>
  
  <pre><code>   ID         xyz
  0  '12345.0'    4.56
  1   NaN        45.60
  2  '54231.0'  987.00
  </code></pre>
  
  <p>Is there an easy way get the ID as a string without decimal like <code>'12345'</code>without having to edit the Strings after importing the table?</p>