title: Create n rows per id | Pandas
body: <p>I have a Dataframe <code>df</code> as follows:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>id</th>
  <th>lob</th>
  <th>addr</th>
  <th>addr2</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>a1</td>
  <td>001</td>
  <td>1234</td>
  <td>0</td>
  </tr>
  <tr>
  <td>a1</td>
  <td>001</td>
  <td>1233</td>
  <td>0</td>
  </tr>
  <tr>
  <td>a3</td>
  <td>003</td>
  <td>1221</td>
  <td>0</td>
  </tr>
  <tr>
  <td>a4</td>
  <td>009</td>
  <td>1234</td>
  <td>0</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>I want to generate <code>n</code> (let's take 4) rows per id, with the other columns being <code>null/na/nan</code> values.
  So, the above table is to be transformed to:</p>
  <div class="s-table-container">
  <table class="s-table">
  <thead>
  <tr>
  <th>id</th>
  <th>lob</th>
  <th>addr</th>
  <th>addr2</th>
  </tr>
  </thead>
  <tbody>
  <tr>
  <td>a1</td>
  <td>001</td>
  <td>1234</td>
  <td>0</td>
  </tr>
  <tr>
  <td>a1</td>
  <td>001</td>
  <td>1233</td>
  <td>0</td>
  </tr>
  <tr>
  <td>a1</td>
  <td>001</td>
  <td>na</td>
  <td>na</td>
  </tr>
  <tr>
  <td>a1</td>
  <td>na</td>
  <td>na</td>
  <td>na</td>
  </tr>
  <tr>
  <td>a3</td>
  <td>003</td>
  <td>1221</td>
  <td>0</td>
  </tr>
  <tr>
  <td>a3</td>
  <td>na</td>
  <td>na</td>
  <td>na</td>
  </tr>
  <tr>
  <td>a3</td>
  <td>na</td>
  <td>na</td>
  <td>na</td>
  </tr>
  <tr>
  <td>a3</td>
  <td>na</td>
  <td>na</td>
  <td>na</td>
  </tr>
  <tr>
  <td>a4</td>
  <td>009</td>
  <td>1234</td>
  <td>0</td>
  </tr>
  <tr>
  <td>a4</td>
  <td>na</td>
  <td>na</td>
  <td>na</td>
  </tr>
  <tr>
  <td>a4</td>
  <td>na</td>
  <td>na</td>
  <td>na</td>
  </tr>
  <tr>
  <td>a4</td>
  <td>na</td>
  <td>na</td>
  <td>na</td>
  </tr>
  </tbody>
  </table>
  </div>
  <p>How can I achieve this? I will have anywhere from 500-700 ids at the time of execution and the n will always be 70 (so each id should have 70 rows).</p>
  <p>I wanted to create a loop that would create a row, do a group by id, see if it's less than 70 and repeat the process but it would end up doing a lot of unnecessary operations.</p>