title: Return a list of words that contain a letter
body: <p>I wanna return a list of words containing a letter disregarding its case. 
  Say if i have <code>sentence = "Anyone who has never made a mistake has never tried anything new"</code>, then <code>f(sentence, a)</code> would return </p>
  
  <pre><code>['Anyone', 'has', 'made', 'a', 'mistake', 'has', 'anything']
  </code></pre>
  
  <p>This is what i have</p>
  
  <pre><code>import re 
  def f(string, match):
      string_list = string.split()
      match_list = []
      for word in string_list:
  
          if match in word:
              match_list.append(word)
      return match_list
  </code></pre>