Differences between two methods of checking for empty strings

Question

What are the differences between the two methods?

if myString == ""

if not myString:

I read Most elegant way to check if the string is empty in Python? before asking, but it doesn't clarify their differences.

I read the post before asking, in that post, it is not clarified their differences. Please feel free to correct me if I am wrong. — Lin Ma
– Lin Ma, Commented Oct 7, 2015 at 7:53
@jonrsharpe was trying to say it was wrong ended up writing that — The6thSense
– The6thSense, Commented Oct 7, 2015 at 7:57
@LinMa both does the same thing the myString == "" checks if string is empty explicitly not myString checks if string is empty implicitly — The6thSense
– The6thSense, Commented Oct 7, 2015 at 8:14
@LinMa by default not "" will be False like wise not [],not 0,not {} etc.. but it is said to use if myString == "" because it is more readable — The6thSense
– The6thSense, Commented Oct 7, 2015 at 8:17
@LinMa I believe they mean just if not '':, not actually referring to myString in that example — jonrsharpe
– jonrsharpe, Commented Oct 7, 2015 at 9:15

jonrsharpe · Accepted Answer · 2015-10-07 08:32:32Z

Both approaches will tell you, given a string object foo, whether it's an empty string or not:

>>> foo = ''
>>> foo == ''
True
>>> not foo
True
>>> foo = 'foo'
>>> foo == ''
False
>>> not foo
False

However, given an arbitrary object bar, you will get different results:

>>> bar = []  # empty list
>>> bar == ''
False  # isn't an empty string
>>> not bar
True  # but is still empty

Testing the truthiness works for many different kinds of object (see the docs), so not x will tell you whenever you have an "empty" object, but x == '' will only tell you whether or not you have an empty string. Which behaviour you need will depend on the situation you're in:

if it's definitely a string and you want to know if it's an empty string, you can use either (but not is neater);
if it's an arbitrary object and you want to know if it's an empty string, you need to use == ''; and
if it's an arbitrary object and you want to know if it's empty, you need to use not.

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