July 2017
Intermediate to advanced
398 pages
11h 54m
Chinese
Content preview from Python数据处理
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18
｜
第
2
章
Python
会返回
0.3
，这也正是我们本来希望看到的值（而不是
0.30000000000000004
）。
我们来一行一行地阅读这三行代码：
from
decimal
import
getcontext, Decimal
➊
getcontext().prec = 1
➋
Decimal(0.1) + Decimal(0.2)
➌
➊
从
decimal
模块中导入
getcontext
和
Decimal
。
➋
将舍入精度设定为一位小数。
decimal
模块将大部分的舍入和精度设置保存在默认的
上
下文
（
context
）中。本行代码将上下文的精度改成只保留一位小数。
➌
对两个小数（一个值为
0.1
，一个值为
0.2
）求和。
如果修改
getcontext().prec
的值会怎么样？动手试一下，然后重新运行最后一行代码。
你应该会看到不一样的结果，这取决于你设置的是保留几位小数。
如前文所述，在数据处理过程中你会遇到许多数学上的细节问题。你可能需要完成的数学
运算也有许多不同的方法，但在用到非整数时，使用小数型数据可以使计算精度更高。
Python
中的数字
Python
中的数字类型有不同的精度水平，这是
Python
语言的缺点之一。随着对数据
处理的深入学习，我们将在本书中学到更多
Python
中与数字和数学相关的库。要是
你现在就想知道，并且打算做一些不那么基础的数学运算，下面是一些你需要熟悉的
Python
库。
•
decimal
（
https://docs.python.org/2/library/decimal.html ...
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