How do you "clear" only specific Flask session variables?

Question

I've seen many examples and questions about clearing a Flask session, but haven't been able to find a clear answer on how to only clear a specific key or set of keys.

If I don't want to clear the entire session, how can I can completely remove (as if it never existed) a specific key?

For example, I want to clear session['foo'], but keep session['bar']. So when I later do:

if 'foo' in session:

This should return False.

Chandu · Accepted Answer · 2018-09-23 06:59:42Z

11

from session.keys() have you tried popping out keys?

# remove the keyname from the session if it is there session.pop('key_name')

answered Sep 23, 2018 at 6:59

Chandu

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5 Comments

Source Matters Over a year ago

Ah ok. This seems to work. Does this have any pros/cons over using "del", for example: del session['foo']

Chandu Over a year ago

Use pop when you need to know the value of deleted key.Use del otherwise.

Source Matters Over a year ago

Good to know. Thanks so much.

Chandu Over a year ago

pop is my way of doing it. avoid del

Chandu Over a year ago

Yes, and it depends upon your knowledge over the application. if you're sure about the session keys and values need not to check but we shouldn't trust the client always better to check if key existed or not then raise Exception.

Abc Xyz · Accepted Answer · 2020-09-04 15:59:52Z

I remember writing app that was poping elements very fast and it behaves weird (dont remember right now this specific case) but I used to use from then del everywhere i could.

If you want to remove key from session if it exist or not you can use pop:

flask.session.pop('key_name', None)

with del it would be:

try: del flask.session['key_name'] except KeyError: pass

I wrote this answer because of CSMaveric comments, about avoiding del.

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