title: Regex pattern to match an alphabet of letters as well as a list of user-specified special characters
body: <p>I am trying to write a regex to filter a pandas column of sentences I have.</p>
  <p>My goal is to capture only english characters like <code>[a-zA-Z]</code> but I would also like to allow some special characters such as apostrophes [']. How can I string this all together in pandas to replace all other special characters, numbers, etc. with blank strings <code>''</code>?</p>
  <p>I'm assuming it's something along the lines of : <code>df['column1'].replace(to_replace = r'[^a-zA-Z]', value = '', regex = True, inplace = True)</code> but I'm new to regex and not sure how to include other characters such as apostrophes.</p>
  <p>An example I would like to scrub:</p>
  <p><code>source = 'i believe that's a dog. isn't it?</code></p>
  <p><code>desired_result = 'i believe that's a dog isn't it</code></p>
  <p>Thanks.</p>