title: Convert columns to string in Pandas
body: <p>I have the following DataFrame from a SQL query:</p>
  
  <pre><code>(Pdb) pp total_rows
       ColumnID  RespondentCount
  0          -1                2
  1  3030096843                1
  2  3030096845                1
  </code></pre>
  
  <p>and I want to pivot it like this:</p>
  
  <pre><code>total_data = total_rows.pivot_table(cols=['ColumnID'])
  
  (Pdb) pp total_data
  ColumnID         -1            3030096843   3030096845
  RespondentCount            2            1            1
  
  [1 rows x 3 columns]
  
  
  total_rows.pivot_table(cols=['ColumnID']).to_dict('records')[0]
  
  {3030096843: 1, 3030096845: 1, -1: 2}
  </code></pre>
  
  <p>but I want to make sure the 303 columns are casted as strings instead of integers so that I get this:</p>
  
  <pre><code>{'3030096843': 1, '3030096845': 1, -1: 2}
  </code></pre>