title: Adding calculated column in Pandas
body: <p>I have a dataframe with 10 columns.  I want to add a new column 'age_bmi' which should be a calculated column multiplying 'age' * 'bmi'.  age is an INT, bmi is a FLOAT. </p>
  
  <p>That then creates the new dataframe with 11 columns.</p>
  
  <p>Something I am doing isn't quite right.  I think it's a syntax issue.  Any ideas?</p>
  
  <p>Thanks</p>
  
  <pre><code>df2['age_bmi'] = df(['age'] * ['bmi'])
  print(df2)
  </code></pre>