如何定义一个十进制类在python中持有1000位数？ [英] How to define a decimal class holding 1000 digits in python?

问题描述

我需要一个拥有1000个十进制数字的类来计算一个系列中的pi数。花时间不重要。如何定义 __ add __ & ...功能这样做？
为例，我需要的值可以保存这个数字：
3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066470938446095505822317253594081284811174502841027019385211055596446229489549303819644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412737245870066063155881748815209209628292540917153643678925903600113

I need a class holding 1000 decimal digits to calculate something like pi number in a series. Taking time is not important. How can I define __add__ & ... functions to do this? For example I need a value can hold this number: 3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066470938446095505822317253594081284811174502841027019385211055596446229489549303819644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412737245870066063155881748815209209628292540917153643678925903600113

：））

使用 decimal.Decimal 的数字显示如下：

from decimal import Decimal as dc
>>> x=dc(3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066470938446095505822317253594081284811174502841027019385211055596446229489549303819644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412737245870066063155881748815209209628292540917153643678925903600113)
>>> x
Decimal('3.141592653589793115997963468544185161590576171875')

但是我需要一个新类保存所有DIGITS我可以使用加法，除法和函数在它像2 + 1和pi数是一个例子，正是我不需要计算pi数字我想计算超大十进制数！

But I need a new class holding all DIGITS and I can use adding, dividing and ... functions in it like 2+1 and pi number is an example of that and exactly I don't need to calculate pi number I wanted to calculate extra large decimal numbers!

推荐答案

您必须设置1000个十进制数字的上下文：

You have to set a context with 1000 decimal digits:

context = decimal.Context(prec=1000)
decimal.setcontext(context)

$ b b

从现在起，计算将使用1000位精度。

From now on computations will use 1000 digits precision.

示例：

>>> decimal.setcontext(decimal.Context(prec=1000))
>>> pi = decimal.Decimal('3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066470938446095505822317253594081284811174502841027019385211055596446229489549303819644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412737245870066063155881748815209209628292540917153643678925903600113')
>>> pi
Decimal('3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066470938446095505822317253594081284811174502841027019385211055596446229489549303819644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412737245870066063155881748815209209628292540917153643678925903600113')
>>> pi + 2
Decimal('5.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066470938446095505822317253594081284811174502841027019385211055596446229489549303819644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412737245870066063155881748815209209628292540917153643678925903600113')

需要注意的是：

Note that:

• 您必须使用字符串来初始化 Decimal ，因为如果使用 float 解释器将必须首先截断它。 （也相信只有最新版本的 decimal 接受一个 float 参数在旧版本中， code> Decimal.from_float ）。


• 计算期间保留小数位数。

• You have to use strings to initialize the Decimal because if you use a float the interpreter will have to truncate it first. (also I believe only the most recent versions of decimal accept a float argument. In older versions you had to use Decimal.from_float instead).
• The decimal digits are preserved during calculations.

您也可以通过 localcontext contextmanager：

You can also use the context locally via the localcontext contextmanager:

context = decimal.Context(prec=1000)

with decimal.localcontext(context):
    # here decimal uses 1000 digits for computations
    pass

# here the default context is restored.

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