title: Setting a constant (date) value for class property
body: <p>I use an incremental backup script which stores new/changed data in a date-stamped directory (e.g. 2022-08-24) via rsync. After completing the backup, a symlink is created as a reference for rsync's <code>--link-dest</code> parameter during the next backup.</p>
  <p>This works reasonably well, unless the backup runs past midnight. In this case, my Backup class' <code>target_dir</code> property returns two different values for the actual target dir and the symlink destination because the <code>datetime.date.today()</code> method is evaluated
  twice:</p>
  <pre><code>@property
  def target_dir(self):
      return f'{self.target_path}/{datetime.date.today().strftime(&quot;%Y-%m-%d&quot;)}'
  </code></pre>
  <p>I obviously need to set a fixed value for the current date for each run, but I wonder whether this should be a class variable or an instance variable (using <code>setattr()</code>). Both methods seem to work fine.</p>
  <p>Any input is appreciated.</p>
  <p>Thanks,
  Jan</p>