title: What does the second argument of the Session.pop method do in Python Flask?
body: <p>I'm working through the Flask tutorial and would just like to clarify exactly what the .pop attr of the session object does and why it would take a 'None' parameter.</p>
  
  <pre><code>@app.route('/logout')
  def logout():
      session.pop('logged_in', None)
      flash('You were logged out')
      return redirect(url_for('show_entries'))
  </code></pre>