Python整数除法产生浮点数

Python 3.1 (r31:73574, Jun 26 2009, 20:21:35) [MSC v.1500 32 bit (Intel)] on win32
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>>> 2/2
1.0

Is this intended? I strongly remember earlier versions returning int/int=int? What should I do, is there a new division operator or must I always cast?

Take a look at PEP-238: Changing the Division Operator

The // operator will be available to request floor division unambiguously.

Oops, immediately found 2//2.

Hope it might help someone instantly.

Behavior of Division Operator in Python 2.7 and Python 3

In Python 2.7: By default, division operator will return integer output.

to get the result in double multiple 1.0 to “dividend or divisor”

100/35 => 2 #(Expected is 2.857142857142857)
(100*1.0)/35 => 2.857142857142857
100/(35*1.0) => 2.857142857142857

In Python 3

// => used for integer output
/ => used for double output

100/35 => 2.857142857142857
100//35 => 2
100.//35 => 2.0    # floating-point result if divsor or dividend real

The accepted answer already mentions PEP 238. I just want to add a quick look behind the scenes for those interested in what’s going on without reading the whole PEP.

Python maps operators like +, -, * and / to special functions, such that e.g. a + b is equivalent to

a.__add__(b)

Regarding division in Python 2, there is by default only / which maps to __div__ and the result is dependent on the input types (e.g. int, float).

Python 2.2 introduced the __future__ feature division, which changed the division semantics the following way (TL;DR of PEP 238):

• / maps to __truediv__ which must “return a reasonable approximation of the mathematical result of the division” (quote from PEP 238)
• // maps to __floordiv__, which should return the floored result of /

With Python 3.0, the changes of PEP 238 became the default behaviour and there is no more special method __div__ in Python’s object model.

If you want to use the same code in Python 2 and Python 3 use

from __future__ import division

and stick to the PEP 238 semantics of / and //.

According to Python3 documentation,python when divided by integer,will generate float despite expected to be integer.

For exclusively printing integer,use floor division method. Floor division is rounding off zero and removing decimal point. Represented by //

Hence,instead of 2/2 ,use 2//2

You can also import division from __future__ irrespective of using python2 or python3.

Hope it helps!