title: How to store formulas, instead of values, in pandas DataFrame
body: <p>Is it possible to work with pandas DataFrame as with an Excel spreadsheet: say, by entering a formula in a column so that when variables in other columns change, the values in this column change automatically? Something like:</p>
  
  <pre><code>a  b  c
  2  3  =a+b
  </code></pre>
  
  <p>And so when I update 2 or 3, the column <code>c</code> also updates automatically.</p>
  
  <p>PS: It's clearly possible to write a function to return <code>a+b</code>, but is there any built-in functionality in pandas or in other Python libraries to work with matrices this way?</p>