Question

This script will run as expected and pass doctests without any errors in Python 2.6:

def num_even_digits(n):
    """
      >>> num_even_digits(123456)
      3
      >>> num_even_digits(2468)
      4
      >>> num_even_digits(1357)
      0
      >>> num_even_digits(2)
      1
      >>> num_even_digits(20)
      2
    """


    count = 0
    while n:
        digit=n%10
        if digit%2==0:
            count+=1
            n/=10
        else:
            n/=10

    return count



if __name__ == '__main__':
    import doctest
    doctest.testmod()

In Python3.0 this is the output:

**********************************************************************
File "/home/calder/My Documents/Programming/Python Scripts/ch06.py", line 3, in                            
 __main__.num_even_digits`
Failed example:
    num_even_digits(123456)
Expected:
    3
Got:
    1
**********************************************************************
File "/home/calder/My Documents/Programming/Python Scripts/ch06.py", line 5, in                   
__main__.num_even_digits
Failed example:
    num_even_digits(2468)
Expected:
    4
Got:
    1
**********************************************************************
1 items had failures:
   2 of   5 in __main__.num_even_digits
***Test Failed*** 2 failures.

I have tried running the Python script “2to3”, but no changes are needed it says. Does anyone know why the script will not run in Python 3?

Answer 1

I’m guessing you need n //= 10 instead of n /= 10. In other words, you want to explictly specify integer division. Otherwise 1 / 10 will return 0.1 instead of 0. Note that //= is valid python 2.x syntax, as well (well, starting with version ~2.3, I think…).