-1/2

[Serve Lau]

What is the expected result of -1/2 in python?

[Christian Heimes]

Re: -1/2

Serve Lau wrote:

What is the expected result of -1/2 in python?

0

Christian

[Gary Herron]

Re: -1/2

Serve Lau wrote:

What is the expected result of -1/2 in python?
>
--
http://mail.python.org/mailman/listinfo/python-list

From the manual:


The result is always rounded towards minus infinity: 1/2 is 0, (-1)/2 is
-1, 1/(-2) is -1, and (-1)/(-2) is 0.


Gary Herron

[Gary Herron]

Re: -1/2

Christian Heimes wrote:

Serve Lau wrote:
>

>What is the expected result of -1/2 in python?
>>

>
0
>
>

No. That's not right. (It would be in C/C++ and many other languages.)

See my other response for the correct answer.

Gary Herron

Christian
>
--

http://mail.python.org/mailman/listinfo/python-list

>

[drobinow@gmail.com]

Re: -1/2

On Jun 22, 2:32 pm, "Serve Lau" <ni...@qinqin.c omwrote:

What is the expected result of -1/2 in python?

I would say -1, but it depends on whether the "-" is a unary minus.

>>-1/2

-1

>>3 -1/2

3

[Terry Reedy]

Re: -1/2



Serve Lau wrote:

What is the expected result of -1/2 in python?

Python 3.0b1 (r30b1:64403M, Jun 19 2008, 14:56:09) [MSC v.1500 32 bit
(Intel)]
n win32
Type "help", "copyright" , "credits" or "license" for more information.

>>-1/2

-0.5
as expected ;-)

-1//2 is as Gary Herron specified from the manual, for reasons posted
here several times and which should be in the FAQ

[Lie]

Re: -1/2

On Jun 23, 1:32 am, "Serve Lau" <ni...@qinqin.c omwrote:

What is the expected result of -1/2 in python?

Operator precedence:
Both python 2 and 3 follows the same rule for operator precedence,
see: http://www.ibiblio.org/g2swap/byteof...recedence.html
. In -1/2, unary negative takes precedence, then division, i.e. it's
interpreted as ((-1) / 2).

Py3k and Python 2 differences:
Before Python 3, integer division is always rounds to minus infinity.
In Python 3, integer division yields floats. To use integer division
in Python 3, you use // operator.

Simple answer:
Python 2: (-1)/2 = round(-0.5) = -1
Py3k: (-1)/2 = float(-1) / float(2) = -0.5

[Duncan Booth]

Re: -1/2

Lie <Lie.1296@gmail .comwrote:

On Jun 23, 1:32 am, "Serve Lau" <ni...@qinqin.c omwrote:

>What is the expected result of -1/2 in python?

>
>
Operator precedence:
Both python 2 and 3 follows the same rule for operator precedence,
see:

http://www.ibiblio.org/g2swap/byteofpython/read/operator-precedence.htm

l . In -1/2, unary negative takes precedence, then division, i.e. it's
interpreted as ((-1) / 2).
>
Py3k and Python 2 differences:
Before Python 3, integer division is always rounds to minus infinity.
In Python 3, integer division yields floats. To use integer division
in Python 3, you use // operator.
>
Simple answer:
Python 2: (-1)/2 = round(-0.5) = -1
Py3k: (-1)/2 = float(-1) / float(2) = -0.5
>

Python 2.x gives -1 or -0.5 depending on the division mode in operation and
for -1 may also generate a deprecation warning:


C:\>python25\py thon -Qnew -c "print -1/2"
-0.5

C:\>python25\py thon -Qwarn -c "print -1/2"
-c:1: DeprecationWarn ing: classic int division
-1


--
Duncan Booth http://kupuguy.blogspot.com