title: Adding new columns to a dataframe
body: <p>I have a list containing the column names of a dataframe. I want to add these empty columns to a dataframe that already exists.</p>
  <pre><code>col_names = [&quot;a&quot;, &quot;b&quot;, &quot;e&quot;]
  df = pd.Dataframe()
  df = # stores some content
  </code></pre>
  <p>I understand a single new column can be added in the following manner and I could do the same for other columns</p>
  <pre><code>df['e'] = None
  </code></pre>
  <p>However, I'd like to know how to add these new columns at once.</p>