Integer division in Python 2 and Python 3

Question

How can I divide two numbers in Python 2.7 and get the result with decimals?

I don't get it why there is difference:

in Python 3:

>>> 20/15
1.3333333333333333

in Python 2:

>>> 20/15
1

Isn't this a modulo actually?

Related: Why does integer division yield a float instead of another integer? — Peter Mortensen
– Peter Mortensen, Commented Jan 30, 2022 at 1:17

Peter Mortensen · Accepted Answer · 2022-02-01 19:03:49Z

138

In Python 2.7, the / operator is integer division if inputs are integers.

If you want float division (which is something I always prefer), just use this special import:

from __future__ import division

See it here:

>>> 7 / 2
3
>>> from __future__ import division
>>> 7 / 2
3.5
>>>

Integer division is achieved by using //, and modulo by using %:

>>> 7 % 2
1
>>> 7 // 2
3
>>>

As commented by user2357112, this import has to be done before any other normal import.

edited Feb 1, 2022 at 19:03

Peter Mortensen

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answered Jan 23, 2014 at 19:01

bgusach

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8 Comments

user2357112 Over a year ago

It's worth noting that future statements have to appear before any other code in a module, particularly before non-future imports. Also, import __future__ doesn't work.

woozyking Over a year ago

Nice. Using __future__ is almost always the recommended way

bgusach Over a year ago

@dumbledad, it is more readable, concise and intuitive

dumbledad Over a year ago

Interesting - I do not find it more intuitive. If I know that / is integer division and the result has decimals I would be taken by suprise, and the from __future__ import division may be more than a screenful away.

bgusach Over a year ago

Well, it is somehow subjective, but for me, coming from other languages, it was confusing that dividing 3/2==1. Many people may agree, because float division is the default in python 3

|

mhlester · Accepted Answer · 2014-01-23 19:05:11Z

67

In Python 3, / is float division

In Python 2, / is integer division (assuming int inputs)

In both 2 and 3, // is integer division

(To get float division in Python 2 requires either of the operands be a float, either as 20. or float(20))

edited Jan 23, 2014 at 19:05

answered Jan 23, 2014 at 18:56

mhlester

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1 Comment

Ivan X Over a year ago

Thanks for the paranthetical -- it was what I was curious about.

woozyking · Accepted Answer · 2014-01-23 19:00:20Z

17

In Python 2.x, make sure to have at least one operand of your division in float. Multiple ways you may achieve this as the following examples:

20. / 15
20 / float(15)

answered Jan 23, 2014 at 19:00

woozyking

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Comments

Peter Mortensen · Accepted Answer · 2022-02-01 19:05:29Z

12

"/" is integer division in Python 2, so it is going to round to a whole number. If you would like a decimal returned, just change the type of one of the inputs to float:

float(20)/15 #1.33333333

edited Feb 1, 2022 at 19:05

Peter Mortensen

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answered Jan 23, 2014 at 19:02

Bryan

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