title: Pandas Dataframe pivoting: making new columns from column values
body: <p>How can I convert <a href="https://i.stack.imgur.com/TgGs8.png" rel="nofollow noreferrer">Original Dataframe</a> to the <a href="https://i.stack.imgur.com/0FQ4Z.png" rel="nofollow noreferrer">Desired Dataframe</a>?</p>
  
  <pre><code>Original DataFrame
  --------------------------------------------------
  | Key | Value | Month              |
  --------------------------------------------------
  | 1       | 123 | 1
  --------------------------------------------------
  | 1       | 456| 2
  --------------------------------------------------
  | 1       | 789| 3
  --------------------------------------------------
  | 2       | 111| 1
  --------------------------------------------------
  | 2       | 222| 2
  --------------------------------------------------
  | 2       | 333| 3
  --------------------------------------------------
  
  Desired DataFrame
  --------------------------------------------------
  | Key | Month_1 | Month_2 | Month_3             |
  --------------------------------------------------
  |1  |123    |456    |789|
  --------------------------------------------------
  |2  |111    |222    |333|
  --------------------------------------------------
  </code></pre>