title: str.contain "\" should only be used as an escape character outside of raw strings
body: <p>I have a dataframe with one column and i want to know if the value of the column contain a &quot;+&quot;. I made like this:</p>
  <pre><code>mask = df['column'].str.contains(&quot;\+&quot;)
  </code></pre>
  <p>But when I execute the sonarqube analysis throws me a bug (&quot;&quot; should only be used as an escape character outside of raw strings).</p>
  <p>I tried to change the line of code to this:</p>
  <pre><code>mask = df['column'].str.contains(r&quot;+&quot;)
  </code></pre>
  <p>But throws me an error:</p>
  <pre><code>re.error: nothing to repeat at position 0
  </code></pre>
  <p>How can i make the same as the first line without the error??</p>