negative number division in Python [duplicate]

Question

Using Python 2.7 and -1/2 will be result in -1, since -1 is floor of -0.5. But I want to get result of 0, which is 1/2 (result in 0), then negative 1/2 (final result still 0) Wondering if there is an elegant way to do this?

My current solution is using abs and check their sign first, which seems not very elegant, wondering if anyone have more elegant solutions?

Source code in Python 2.7,

a = -1
b = 2
print a/b # output -1
# prefer -(1/2) = 0

r = abs(a)/abs(b)
if (a > 0 and b < 0) or (a < 0 and b > 0):
    r = -r
print r

This answer is elegant because you do not really on floating point arithmetic or sign functions stackoverflow.com/questions/1986152/… — Elmex80s
– Elmex80s, Commented Feb 23, 2017 at 2:19
@Elmex80s, thanks. For "this answer", which answer do you mean? — Lin Ma
– Lin Ma, Commented Feb 23, 2017 at 23:28

kindall · Accepted Answer · 2017-02-23 02:04:44Z

1

Do the division, then do it again your way if it came out negative.

r = a / b
r = -(abs(a) / abs(b)) if r < 0 else r

answered Feb 23, 2017 at 2:04

kindall

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2 Comments

kingstante Over a year ago

Or use reverse floor division..

Lin Ma Over a year ago

Thanks kindall, like your method and vote up. It looks like no straightforward solution in Python?

DYZ · Accepted Answer · 2017-02-23 02:08:12Z

1

First check the signs, then divide:

r = a/b if ((a >= 0) ^ (b < 0)) else -a/b

answered Feb 23, 2017 at 2:08

DYZ

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8 Comments

Lin Ma Over a year ago

Thanks DYZ, vote up and could you explain a bit more what is your purpose of (a >= 0) ^ (b < 0)?

DYZ Over a year ago

This expression is True if and only if both a and b have the same sign.

Lin Ma Over a year ago

Thanks DYZ, ^ is XOR, it should operate on bits, but (a>=0) or (b<0) returns True or False, how do you do XOR on True and False?

DYZ Over a year ago

True is 1, and False is 0.

AnukuL Over a year ago

@DYZ You may wanna fix your expression, this wouldn't work when a < 0 and b > 0, for ex: a = -1 and b = 2

|

Community · Accepted Answer · 2017-05-23 12:16:53Z

-1

What about this

int(a / float(b))

The int function does the trick:

>>> int(-0.999)
0
>>> int(0.999) 
0

I see that is also one of the answers to this question In Python, what is a good way to round towards zero in integer division?

edited May 23, 2017 at 12:16

CommunityBot

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answered Feb 23, 2017 at 2:10

Elmex80s

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2 Comments

TigerhawkT3 Over a year ago

The int function does not do the trick for e.g. int(-1/2) in Python 2.

Elmex80s Over a year ago

@TigerhawkT3 You should do int(-1/float(2)) which does work in Python 2.7!

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