title: Python regexes: return a list of words containing a given substring
body: <p>What would be a function <code>f</code> based on regexes that, given an input text and a string, returns all the words containing this string in the text. For example:</p>
  
  <pre><code>f("This is just a simple text to test some basic things", "si")
  </code></pre>
  
  <p>would return:</p>
  
  <pre><code>["simple", "basic"]
  </code></pre>
  
  <p>(because these two words contain the substring <code>"si"</code>)</p>
  
  <p>How to do that?</p>