将 int 转换为双 Python
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Convert int to double Python
提问by The Nightman
I can't seem to find the answer to this on this site, though it seems like it would be common enough. I am trying to output a double for the ratio of number of lines in two files.
我似乎无法在这个网站上找到这个问题的答案，尽管这似乎很常见。我正在尝试为两个文件中的行数之比输出一个双精度值。
#Number of lines in each file
inputLines = sum(1 for line in open(current_file))
outputLines = sum(1 for line in open(output_file))
Then get the ratio:
然后得到比例：
ratio = inputLines/outputLines
But the ratio always seems to be an int and rounds even if I initialize it like:
但即使我将其初始化为：
ratio = 1.0
Thanks.
谢谢。
采纳答案by goncalopp
In python 2, the result of a division of two integers is always a integer. To force a float division, you need to use at least one float in the division:
在 python 2 中，两个整数相除的结果总是一个整数。要强制进行浮点除法，您需要在除法中至少使用一个浮点数：
ratio = float(inputLines)/outputLines
ratio = float(inputLines)/outputLines
Be careful not to do ratio = float(inputLines/outputLines): although that results in a float, it's one obtained afterdoing the integer division, so the result will be "wrong" (as in "not what you expect")
注意不要这样做ratio = float(inputLines/outputLines)：虽然这会导致浮点数，但它是在进行整数除法后获得的，因此结果将是“错误的”（如“不是您期望的”）
In python 3, the integer division behavior was changed, and a division of two integers results in a float. You can also use this functionality in python 2.7, by putting from __future__ import divisionin the begging of your files.
在 python 3 中，整数除法行为发生了变化，两个整数的除法导致浮点数。你也可以在 python 2.7 中使用这个功能，通过放入from __future__ import division你的文件中。
The reason ratio = 1.0does not work is that types (in python) are a property of values, not variables- in other words, variables don't have types.
原因ratio = 1.0不起作用是类型（在python中）是values的属性，而不是变量- 换句话说，变量没有类型。
a= 1.0 # "a" is a float
a= 1 # "a" is now a integer
回答by Mihai Maruseac
You need to cast one of the terms to a floating point value. Either explicitly by using float(that is ratio = float(a)/bor ratio=a/float(b)) or implicitly by adding 0.0: ratio = (a+0.0)/b.
您需要将其中一项转换为浮点值。显式地使用float（即ratio = float(a)/b或ratio=a/float(b)）或隐式地添加0.0: ratio = (a+0.0)/b。
If using Python 2 you can from __future__ import divisionto make division not be the integral one but the float one.
如果使用 Python 2，您可以from __future__ import division使除法不是整数而是浮点数。
回答by Underyx
Indeed, Python 2 returns an integer when you divide an integer. You can override this behaviour to work like in Python 3, where int / int = floatby placing this at the top of your file:
事实上，当你除以一个整数时，Python 2 返回一个整数。您可以覆盖此行为以像在 Python 3 中一样工作，int / int = float通过将其放置在文件顶部：
from __future__ import division
Or better yet, just stop using Python 2 :)
或者更好的是，停止使用 Python 2 :)
回答by adrianus
Are you using Python 2.x?
你在使用 Python 2.x 吗？
Try using
尝试使用
>>> from __future__ import division
>>> ratio = 2/5
0.4
to get a floatfrom a division.
float从一个部门得到一个。
Initializing with ratio = 1.0doesn't work because with ratio = inputLines/outputLinesyou are re-assigning the variable to int, no matter what it was before.
初始化ratio = 1.0不起作用，因为ratio = inputLines/outputLines你正在将变量重新分配给 int，无论它之前是什么。
