Negative integer division surprising result

In my application I encountered the following and was surprised by the resu开发者_运维百科lts:

8/-7=-2 (both integers).

What does this mean?

For the actual values, i.e. 8.0/(-7.0), the result is roughly -1.143.

Your result using integer division is being rounded down toward the more negative value of -2. (This is also known as "Floor division")

This is why you will get the somewhat perplexing answers of:

>>> 8/(-7)
-2
>>> 8/7
1

Note: This is "fixed" in Python 3, where the result of 8/(-7) would be -1.143. So if you have no reason to be using Python 2, you should upgrade. ;)

In Python 3, if you still want integer division, you can use the // operator. This will give you the same answer as 8/(-7) would in Python 2.

Here's a Python Enhancement Proposal on the subject: PEP 238 -- Changing the Division Operator

Python always does the "floor division" for both negative numbers division and positive numbers division.

That is

1/10 = 0
1/-10 = -1

But sometime we need 1/-10 to be 0

I figure out it can be done by using the float division first then cast result to int, e.g.

int(float(1)/-10) = 0

That works fine for me, no need to import the future division or upgrade to Python 3

Hope it can help you~

To have Python automatically convert integer division to float, you can use:

from __future__ import division

Now:

8/-7=-1.1428571428571428

This feature is not in the standard Python 2 not to break existing code that relied on integer division.

However, this is the default behavior for Python 3.

When both values are integers when dividing Python uses Floor division.

In Python, / operator is for integer division. You can look at it as float division followed by a floor operation.

For example,

8/7 == floor(8.0/7.0) == 1

8/-7 == floor(8.0/-7.0) == -2