How to check if a string is null in python

Question

I have a value cookie that is returned from a POST call using Python.
I need to check whether the cookie value is empty or null. Thus I need a function or expression for the if condition. How can I do this in Python? For example:

if cookie == NULL

if cookie == None

P.S. cookie is the variable in which the value is stored.

You need to describe what function you use for getting your cookie value: this will tell us what to test for (`None` value? empty string only?). — Eric O Lebigot, Feb 14 '13 at 14:07

Óscar López · Accepted Answer · 2013-02-14T14:26:03.227

26

Try this:

if cookie and not cookie.isspace():
    # the string is non-empty
else:
    # the string is empty

The above takes in consideration the cases where the string is None or a sequence of white spaces.

edited Feb 14 '13 at 14:26

answered Feb 14 '13 at 14:00

Óscar López

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`cookie.isspace()` is more efficient than using `strip` – John La Rooy Feb 14 '13 at 14:10
@gnibbler you're right, I updated my answer. Thanks! – Óscar López Feb 14 '13 at 14:26

score 5 · Answer 2 · answered Feb 14 '13 at 14:00

5

In python, bool(sequence) is False if the sequence is empty. Since strings are sequences, this will work:

cookie = ''
if cookie:
    print "Don't see this"
else:
    print "You'll see this"

answered Feb 14 '13 at 14:00

mgilson

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what if you have have - cookie = "null" then bool(cookie) return True. – suprita shankar Mar 28 '16 at 08:26
what's the difference in functionality between `if cookie` and `if cookie == ""`? – NoName Feb 08 '20 at 23:20
Although the answer is valid for the grand majority of cases, the OP wanted to check if the string was `None` or empty (containing whitespace), e.g. `' '` or `'\n\t'`. – StickySli Jun 04 '22 at 18:26

How to check if a string is null in python

2 Answers2