Why does Python 3.4 give the wrong answer for division of large numbers, and how can I test for divisibility?
division, floating-point, precision, python
Solution
The floating-point result is wrong because dividing two ints with `/` produces a float, and the exact result of your division cannot be represented exactly as a `float`. The exact result 11882227807719423 must be rounded to the nearest representable number:
In [1]: float(11882227807719423)
Out[1]: 1.1882227807719424e+16
Problem
In my program, I'm using division to test if the result is an integer, I'm testing divisibility. However, I'm getting wrong answers. Here is an example: ``` print(int(724815896270884803/61)) ``` gives 11882227807719424. ``` print(724815896270884803//61) ``` gives the correct result of 11882227807719423. Why is the floating point result wrong, and how can I test whether the large number is divisible by 61? Do I really need to do integer division and then multiply it back and see if it's equal?