title: Regex Python extract digits between two strings in a single expression
body: <p>I want only digits existing between two characters in order to get an integer dollar value, e.g. from string:</p>
  
  <p><code>"Advance [Extra Value of $1,730,555] in packages 2,3, and 5."</code></p>
  
  <p>we want to obtain <code>"1730555"</code>.</p>
  
  <p>We can use <code>\$(.*)\]</code> to get <code>"1,730,555"</code>, but how do we remove the commas in the same expression, while retaining the possibility of arbitrary many commas, ideally getting the number in a single capturing group?</p>