python basic code printed differently

Question

[Basically the professor from the video is testing the exact same basic code but his one is printed is "Odd" while my python program is printed "Even" which should be printed "Even" why it is printed differently when using the exact same code?

The video link is here https://youtu.be/Pij6J0HsYFA?t=1942 ]1

x = 15
if (x/2)*2 == x:
 print('Even')
else: print('Odd')

• JCVanHamme: It's probably a difference between division behavior in Python 2 vs. 3. In 2, x / 2 is assumed to be integer division, while in 3 it's float division by default.
• Steven Summers: The video uses python2 while you are using python3
• ZdaR: Python has % (modulo) operator which may save your time from writing if (x/2)*2 == x:
• Jean-François Fabre: I thought of that, but even in python 3, >>> x=100000000000000 >>> (x/2)*2 == x True, even float divide+multiply still is equal (I would bet on that)
• Cribber: from the looks of the code it should be "odd" (it would be even if you would cast x as a float - which is why there is a python function for testing if a number is even or odd). try printing (x/2)*2 => if its 15, then there is a hidden float cast - which python version are you using? 2.7 or 3.x?

Answer 1

Integer division behaves differently in Python 2.7 and Python 3.X.

C:\Users\Kevin\Desktop>py -2
Python 2.7.11 (v2.7.11:6d1b6a68f775, Dec 5 2015, 20:32:19) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> 15/2
7
>>> (15/2)*2
14
>>> ^Z
C:\Users\Kevin\Desktop>py -3
Python 3.5.1 (v3.5.1:37a07cee5969, Dec 6 2015, 01:38:48) [MSC v.1900 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> 15/2
7.5
>>> (15/2)*2
15.0
>>>

The professor is probably using 2.7, and you're probably using 3.X.

In any case, it's much better to use modulus to check the evenness of a number, since it doesn't depend on version-specific behavior.

>>> def is_even(x):
... return x%2 == 0
...
>>> is_even(15)
False
>>> is_even(16)
True
>>> is_even(17)
False

• Mad Physicist: Thanks for mentioning that this is stupid to begin with (+1).

Answer 2

Because the lecturer is using Py2 and you are using Py3.

In Python 2, the result of dividing integers is an integer, which gets truncated: 15 / 2 == 7. Since 7 * 2 != 15, the lecturer prints Odd.

In Python 3, the result of dividing integers is a float if need be to preserve the actual value: 15 / 2 == 7.5, so you print Even.

The equivalent Py3 operation to preserve the type and floor the result would be 15 // 2 == 7.

Answer 3

The difference is due to Python2 and Python3.

In Python 3.0, 5 / 2 will return 2.5 .The same in Python2 would generate 2.

The former being floating point division and other integer division.

In the code you mentioned,(15/2)*2 is 14 as 7 is being generated as floor value not 7.5 which is not equal to 15.Hence it will print Odd,due to python2.

On the other hand,your code will generate (15/2)*2 as 15 due to floating point precision and hence print Even. due to python3.