Modern Python Standard Library Cookbook

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When working with cookies, one particular condition you should pay attention to is their life cycle.

Cookies can have an Expires attribute, which will state on which date they should die (the browser will discard them), and actually, that's the way you delete a cookie. Setting a cookie again with an Expires date in the past will delete it.

But cookies can also have a Max-Age attribute, which states how long they should stick around or can be created as session cookies that will disappear when the browser window is closed.

So, if you face problems with your cookies randomly disappearing or not being loaded back correctly, always check those properties as the cookie might just have been deleted by the browser.