Difference in long int division in python 3

Question

I came across a bizarre situation while doing some large number division in python.

int(1012337203685477580 / 2) = 506168601842738816

and

int(1012337203685477580 >> 1) = 506168601842738790

Why is there a difference between the two approaches? int() appears to be at the least int64 because int(2^63 - 1) and 2^63 - 1 are the same values.

Why did you call `int`? Take those calls out; they're hiding the source of the problem. — user2357112, Sep 10 '16 at 04:05
Also, see this question: http://stackoverflow.com/q/20810729 — , Sep 10 '16 at 04:08

score 4 · Accepted Answer · 2016-09-10T04:12:09.770

4

In Python 3, / is true division, so you will get a floating point result, and all the accuracy problems that entails. Use // for integer division instead:

>>> 1012337203685477580 / 2
5.061686018427388e+17
>>> 1012337203685477580 // 2
506168601842738790
>>> 1012337203685477580 >> 1
506168601842738790

edited Sep 10 '16 at 04:12

answered Sep 10 '16 at 04:03

That's it! Thanks for the answer. It was driving me nuts! :) – sandeeps Sep 10 '16 at 04:12

Difference in long int division in python 3

1 Answers1