How to calculate a mod b in Python?

Question

Is there a modulo function in the Python math library?

Isn't 15 % 4, 3? But 15 mod 4 is 1, right?

You're probably thinking that (15 mod 4 = -1) which is the same as saying (15 mod 4 = 3) — Nathan Fellman, Jun 13 '09 at 17:03
Beware: (-41) % 3 == -2 in C, but (-41) % 3 == 1 in Python http://stackoverflow.com/questions/828092/python-style-integer-division-modulus-in-c — jfs, Jun 13 '09 at 18:19

score 258 · Accepted Answer · answered Jun 13 '09 at 16:59

258

There's the % sign. It's not just for the remainder, it is the modulo operation.

answered Jun 13 '09 at 16:59

eduffy

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score 60 · Answer 2 · edited Jul 28 '19 at 15:58

60

you can also try divmod(x, y) which returns a tuple (x // y, x % y)

edited Jul 28 '19 at 15:58

wjandrea

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answered Jun 14 '09 at 10:58

uolot

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score 43 · Answer 3 · answered Jun 13 '09 at 17:06

43

>>> 15 % 4
3
>>>

The modulo gives the remainder after integer division.

answered Jun 13 '09 at 17:06

Bill the Lizard

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score 27 · Answer 4 · edited Jul 28 '19 at 16:12

27

mod = a % b

This stores the result of a mod b in the variable mod.

And you are right, 15 mod 4 is 3, which is exactly what python returns:

>>> 15 % 4
3

a %= b is also valid.

edited Jul 28 '19 at 16:12

wjandrea

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answered Jun 13 '09 at 17:00

Merijn

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score 11 · Answer 5 · answered Jun 13 '09 at 16:59

11

Why don't you use % ?


print 4 % 2 # 0

answered Jun 13 '09 at 16:59

Geo

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UnsignedByte · Answer 6 · 2017-08-23T22:37:11.573

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I don't think you're fully grasping modulo. a % b and a mod b are just two different ways to express modulo. In this case, python uses %. No, 15 mod 4 is not 1, 15 % 4 == 15 mod 4 == 3.

edited Aug 23 '17 at 22:37

answered Dec 22 '16 at 01:54

UnsignedByte

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score 2 · Answer 7 · edited Jul 28 '19 at 15:59

2

A = [3, 1, 2, 4]
for a in A:
    print(a % 2)

output:

edited Jul 28 '19 at 15:59

wjandrea

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answered Dec 26 '18 at 18:13

Nehal Pawar

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How to calculate a mod b in Python?

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