Why does Python convert 0's into None objects?

Question

I don't quite understand why Python will automatically convert any 0 returned to me by a function into a None object. I've programmed in almost all of the common languages, yet I've never come across this before. I would expect that if I set 0 in the result, I would get 0 back from the function.

Could anyone please explain why Python does this?

EDIT:

To give some more information, we have a wrapper around a C++ class and the return value type is a void pointer. So if it is returning an integer with a value of 0, it gives me a None type. Does this make sense to anyone?

I'm just new to Python and trying to figure out when I might expect None types rather than the return value.

Wish I could give a runnable example, but I can't release the proprietary code that we use. — Brandon, Aug 24 '12 at 21:11
Ah. It sounds like your question is really about whatever technology you're using to do the wrapping (Cython? ctypes? SWIG? something else?), rather than about Python itself. Do you know what's being used here? Some example code would really help, too. — Mark Dickinson, Aug 24 '12 at 21:14
+plus as I did silly mistake in my code and took some time to fix issue — user765443, Apr 16 '15 at 11:57

score 5 · Accepted Answer · edited May 23 '17 at 12:07

5

we have a wrapper around a C++ class and the return value type is a void pointer. So if it is returning an integer with a value of 0, it gives me a None type

0 is the value of the NULL pointer in C++ (although you should refer to it as NULL).

If you have a C++ function returning void* type and you return 0, you're effectively returning NULL, therefore you're returning None in Python.

You may be interested in this question: Do you use NULL or 0 (zero) for pointers in C++? (see nullptr too).

edited May 23 '17 at 12:07

Community

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answered Aug 24 '12 at 20:58

Bruno

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haha well duh... thanks for the info, can't believe that didn't occur to me – Brandon Aug 24 '12 at 21:13

score 4 · Answer 2 · answered Aug 24 '12 at 20:56

Just a wild guess, but if you're doing something like this:

def gives_none()
    #does stuff
    0

you've failed to realize that python needs an explicit return statement. While some languages will return zero here, that's not how Python works. Without an explicit return statement your function will return None. Try:

def works():
    #does stuff
    return 0

score 1 · Answer 3 · answered Aug 24 '12 at 20:57

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Python doesn't enforce return types like Java so it is actually "quite easy" to forget to put in a return statement at the end of a function. This will cause the function to return None.

answered Aug 24 '12 at 20:57

Matti Lyra

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Why does Python convert 0's into None objects?

3 Answers3