title: Display value of a column after checking boolean value of another column - pandas
body: <p>I have a pandas dataframe:</p>
  <pre><code>    pd.DataFrame({
      'total_discounted_cost_bef_929': [490, 0, 490, 0],
      'total_discounted_cost_aft_929': [525, 0, 525, 0],
      'aft_929_bool': [False, False, True, True]
  })
  </code></pre>
  <p>I want to create a new column called 'final_cost'. If 'aft_929_bool' == False, I want the output to be the value in the 'total_discounted_cost_bef_929' column. And the opposite for any True value.</p>