title: How to add values from one column to timestamp column as days?
body: <p>I have a table df:</p>
  <pre><code>date                     day       
  2021-07-25                1 
  2021-07-29                1 
  2021-07-30                1 
  </code></pre>
  <p>I want to filter it this way:</p>
  <pre><code>df[df['device_install_date'] + df['lifetime'] &lt; '2021-07-27']
  </code></pre>
  <p>But it brings error:</p>
  <pre><code>TypeError: can only concatenate str (not &quot;int&quot;) to str
  </code></pre>
  <p>How can I do that? values in day column should add as days to date. <code>Column day has type pandas.core.series.Series</code></p>