Difference between Python 2.6.4 and Python 3.1.2 integer handling

Question

Why does

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

Evaluate to Odd in Python 2.6.4?

While in 3.1.2 (with parentheses around print statements of course) is evaluates to Even?

Answer 1

In Python 2.x, the / operator uses integer division by default. Since Python 3.x (or if you start your 2.x program with from __future__ import division), the / operator performs floating-point division. This is documented in PEP238.

You should use // if you want integer division, or start your programs with from __future__ import division if you want floating point division under 2.x.

Note that the generic way to check whether a number is even or odd is modulo division with the % operator; like this:

x = 15
print ('even' if x % 2 == 0 else 'odd')

For details on these and other operators, refer to the Python manual.