Python - How to get a function to actually return `None`?

Question

Output for:

def test(c):
    if c == 4:
       return None
    return 'test'

returns 'test' given anything I put in such as test(500) but when I try test(4) the function simply skips and pretends I never ran it, but I want it to show None. So,

>> test(500)
'test'
>> test(4)
>>

is what happens. My goal is for a None to return without having to use print in the function:

>> test(4)
None

Help!

But it does return `None`. It just happens to not show that to you, but the return value is indeed `None`. — univerio, May 09 '15 at 02:47
You can confirm it's returning None by doing `print test(4)` then you'll see the `None` return value that is there as others have indicated — Eric Renouf, May 09 '15 at 02:48
The title of my canonical doesn't mention this specific case, but the Q&A covers it. (The title is already quite long, so I couldn't figure out a way to work it in.) The general question is about *how the REPL handles the result of expressions*; it doesn't print `None` results, but it does print others. — Karl Knechtel, Jan 28 '23 at 21:31

score 3 · Answer 1 · answered May 09 '15 at 02:47

3

It is returning None. Nothing is printed, because the output shows the result, which is None, which is nothing, so it is not shown.

answered May 09 '15 at 02:47

holtc

1,780
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score 2 · Answer 2 · answered May 09 '15 at 02:49

2

It is returning None. If you want to see that this is true without putting print in the method definition, you can do this:

print test(4)
> None

answered May 09 '15 at 02:49

leekaiinthesky

5,413
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score 1 · Accepted Answer · answered May 09 '15 at 03:04

None is the result returned by things that "don't return anything", like list.sort or the Python 3 print function. If an expression you type at the interactive prompt evaluates to None, Python won't automatically print it, since it thinks you probably called a "doesn't return anything" function, and it would be confusing to have sessions like

>>> l = [3, 2, 1]
>>> l.sort()
None
>>> print(l)
[1, 2, 3]
None

If you want to print it anyway, you need to explicitly print it.

Python - How to get a function to actually return `None`?

3 Answers3