title: How to extract variables from boolean logic expression in python
body: <p>I want to extract variables from boolean logic expression</p>
  
  <p>ex)<br />
  Input: <code>E= A or B or (C and not D) -&gt; String</code> <br />
  Output: <code>['E', 'A', 'B', 'C', 'D'] -&gt; List</code><br /></p>