How to test for an an empty Redis key in python

Question

I am using redis-py (https://redis-py.readthedocs.org/en/latest/).

lets say I have some redis keys saved and av. 'av' has no assigned value so using the command line, I can do:

>>> redis.get('saved')
Out[4]: 'None'
>>> redis.get('av')
>>> redis.get('saved')
Out[6]: 'None'

How would you test for 'no assigned value' for a key in this context?

I'm not sure I follow. Does 'redis.get('av')' evaluate to False? — user1592380
– user1592380, Commented Jul 7, 2015 at 17:41
@user61629 It looks like if it doesn't find the key it returns None, which would be in line with how get() works for dicts (this get() is probably inherited from dict). Run this and see what it says: redis.get('av') is None — kylieCatt
– kylieCatt, Commented Jul 7, 2015 at 20:32

Jundiaius · Accepted Answer · 2018-08-17 15:59:59Z

40

You should use the method exists, which returns a boolean - True if your key is set, False otherwise. You should avoid the use of get for that, as it can raise an exception if you have a list value for that key.

Example:

>>> redis.exists("av")
False

answered Aug 17, 2018 at 15:59

Jundiaius

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2 Comments

Daniel Waltrip Over a year ago

With redis v3.0, it no longer returns a boolean. It now returns the number of keys that were found in the db, as you can now pass multiple keys to exists. As 0 is falsey in python, most code should still work, but it is good to know about this change.

Callam Delaney Over a year ago

Exceptions are clearer, the fact that something raises an exception is not an issue and can in fact be desired.

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