Idiomatic Python - checking for zero

Question

What is the idiomatic way for checking a value for zero in Python?

if n == 0:

or

if not n:

I would think that the first one is more in the spirit of being explicit but on the other hand, empty sequences or None is checked similar to the second example.

The last line answered your question. What else do you expect? — thefourtheye, May 12 '14 at 13:31
Using the second should be avoided because someone might think n is being checked for None'ness. — Roy Iacob, May 12 '14 at 13:33
@RoyIacob `None` should be tested with `is not None`, per [PEP-008](http://legacy.python.org/dev/peps/pep-0008/#programming-recommendations). — jonrsharpe, May 12 '14 at 13:35

score 4 · Accepted Answer · answered May 12 '14 at 13:34

4

If you want to check for zero, you should use if n == 0. Your second expression doesn't check for zero, it checks for any value that evaluates as false.

I think the answer lies in your requirements; do you really want to check for zero, or do you want to handle a lot of situations where n might be a non-numeric type?

In the spirit of answering exactly the question asked, I think n == 0 is the way to go.

Here's what's wrong with doing it the not n route:

>>> def isZero(n):
...    return not n;
... 
>>> 
>>> isZero([])
True
>>> isZero(False)
True
>>> isZero("")
True
>>>

Most people would say that this "isZero" function isn't correct.

answered May 12 '14 at 13:34

FrobberOfBits

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Why would one put a `;` behind a line in Python? – glglgl Jan 25 '16 at 12:09
1

That's easy; one would put a `;` behind a line of python because one is working in a lot of languages at the same time and gets them mixed up easily! – FrobberOfBits Jan 26 '16 at 13:45

score 3 · Answer 2 · answered May 12 '14 at 13:35

I'm a big proponent of say what you mean. Your two statements mean different things. The first means:

if n equals 0

whereas the second means:

if the truth value of n is False

While they have the same effect in practice for integers, the actual meaning should dictate which you use.

Idiomatic Python - checking for zero

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