python - 处理没有四舍五入、两位小数和千位分隔符的货币的通用方法

Question

我是一名学习 Python (2.7.3) 的新手，接受了一项计算成本的简单练习，但很快就对真正能够控制或理解所产生结果的“准确性”产生了兴趣。如果我在我的电脑上使用计算器，我会得到我认为我想要的结果(即它们看起来非常具体)，但是如果我使用 python，我似乎必须非常准确地了解如何将格式信息添加到正在使用的值中，并且打印。

我的问题的简短版本是:

有没有一个简单的解决方案，我可以在使用返回的货币时使用:

• 小数点后两位小数
• 不进行四舍五入(即基本上只是“截断”小数点后第二位右边的任何内容)
• 必要时添加千位分隔符

如果有人想运行它以查看结果和变化，我一直在与解释器(见下面的代码)测试变化。

谢谢。

# basic entry - both are seen as integers
print 'A:  ', 7/3

# test by printing out the types
print 'B:  ', type(7)
print 'C:  ', type(3)

# this is not necessary as they are already integers
print 'D:  ', int(7/3)

# converts the result of 7/3 into a floating number
print 'E:  ', float(7/3)

# defines the float version of 7 by the float version of 3
print 'F:  ', float(7) / float(3)

# coverts the results of the above into a string and assigns to variable
string_var = str(float(7) / float(3))

# print the string
print 'G:  ', string_var

# prints 4 characters of the string, but returns two decimal places
print 'H:  ', string_var[:4]

string_var = str(25.8545678888)

# prints 5 characters of the string, but returns two decimal places
print 'I:  ',string_var[:5]

# import the locale module
import locale
# sets to user's default settings (don't know what empty quotes are)
locale.setlocale( locale.LC_ALL, '' )

#set an arbitrary float number to a variable
float_var = 25.859

# apply locale.currency formatting
print 'J:  ',locale.currency(float_var)

# import the decimal module
from decimal import *

# the decimal version of the variable
print 'K:  ',Decimal(float_var)

# divide the decimal version by 2
print 'L:  ',Decimal(float_var) / 2

# divide the decimal version by the decimal verson of 2
print 'M:  ', Decimal(float_var) / Decimal(2)

# change decimal precision to 6
getcontext().prec = 6

# note there is no change in this value as precision only applied to
# result of calculations, see
#http://stackoverflow.com/questions/6483440/python-decimal-precision
print 'N:  ', Decimal(float_var)

# the following equation returns decimal precision to 6 (6 characters displayed)
print 'O:  ', Decimal(float_var) / 2

# example of 6 characters printed, not decimal places
# to the right of the decimal
print 'P:  ', Decimal(55550) / 130

# if you want to control places to the right of the decimal
# displayed without rounding and show thousand separators if
# necessary ?

编辑:

感谢大家的回复，这是我采用的解决方案，它是所有回复的混合体:

def make_it_money(number):
    """
    always:
    - shows 2 decimal places
    - shows thousands separator if necessary
    - retains integrity of original var for later re-use
    - allows for concise calling
    """
    import math
    return '$' + str(format(math.floor(number * 100) / 100, ',.2f'))

# tests

var1 = 25.867
var2 = 25.864
var3 = 25.865
var4 = 2500.7869

print make_it_money(var1)
print make_it_money(var2)
print make_it_money(var3)
print make_it_money(var4)

Answer 1

使用 format() function格式化 float 或 Decimal 类型:

format(value, ',.2f')

结果是:

>>> format(12345.678, ',.2f')
'12,345.68'

, 在输出中添加一个逗号作为千位分隔符。

您通常不想在 float 或Decimal 计算后不加选择地向下舍入。如果您觉得您必须无论如何都要这样做，请在格式化之前明确地这样做:

>>> import math
>>> format(math.floor(12345.678 * 100) / 100, ',.2f')
'12,345.67'