and operator with random

Question

i dont understand why the code bellow doesnt work properly. If both variables a and b < 0 it should print that both numbers are negative,else the last message. But it just dont work so, what am i doing wrong? please help!

import random
while True:
    input()
    a=random.randint(-9,9)
    b=random.randint(-9,9)
    print(a,b)
    if a and b < 0:
        print("2 negative numbers:",a,b)
    else:
        print("one or both of the numbers are positive!")

I'm running this on python 3.4.

possible duplicate of [How do I test one variable against multiple values?](http://stackoverflow.com/questions/15112125/how-do-i-test-one-variable-against-multiple-values) — jonrsharpe, May 24 '15 at 10:02

MMaazQ · Answer 1 · 2015-05-26T08:56:31.593

1

Evaluating Both Operands will resolve the issue. Here both Operands are expressions which results in true or false, so if both result in true; you will get your required result.

if ((a < 0) and (b < 0)):

edited May 26 '15 at 08:56

answered May 24 '15 at 10:11

MMaazQ

43
7

2

Hi and welcome to stackoverflow. Although this may be helpful for the question, the answer is not following the expected format for this site. I would recommend you to provide more information on why this answer is helpful. – Wtower May 24 '15 at 10:37

score 1 · Answer 2 · answered May 24 '15 at 10:32

I think you're a little confused about how operators distribute.

When you have

if a and b < 0

it doesn't mean

if (both a and b) < 0

but instead

if (a) and (b < 0)

which is equivalent to

if (a != 0) and (b < 0)

since "numeric zero of all types ... evaluates to false" (see the reference on booleans on docs.python.org)

Instead, you want

if a < 0 and b < 0

which will tell you if both a and b are less than zero.

score 0 · Answer 3 · answered May 24 '15 at 09:59

0

You are evaluating just a, not it's relation to 0:

if a < 0 and b < 0:

answered May 24 '15 at 09:59

Mureinik

297,002
52
306
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score 0 · Answer 4 · answered May 24 '15 at 10:03

0

This:

a and b < 0:

Is equivalent to this:

(a) and (b < 0):

(a) is False when a equals 0 and True otherwise. Therefore, due to short-circuiting b < 0 isn't even evaluated.

As a fix you may use all method:

all(i < 0 for i in (a, b))

answered May 24 '15 at 10:03

Łukasz Rogalski

22,092
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and operator with random

4 Answers4