使用货币的通用方法,没有舍入,两个小数位和数千个分隔符

Question

我是一个新手学习python(2.7.3),并给了一个简单的练习计算成本,但很快就开始对真正能够控制或理解正在生成的结果的"正确性"感兴趣.如果我在我的计算机上使用计算器我得到的结果我认为我在追求(即它们看起来非常具体),但如果我使用python似乎我必须非常准确地说我如何将格式信息添加到正在使用的值和打印.

我的问题的简短版本是:

是否有一个简单的解决方案,我可以使用每当我使用返回的货币时:

• 小数点右边的两个小数位
• 没有四舍五入(即基本上只是'截断'小数点后第二位右边的任何内容)
• 如有必要,增加千位分隔符

如果有人想要运行它以查看结果和变化,我一直在使用解释器(见下面的代码)来测试变化.

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,这是我使用的解决方案,这是所有回复的混合:

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

使用该format()函数格式化float或输入Decimal:

format(value, ',.2f')

这导致:

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

在,增加了一个逗号作为输出千位分隔符.

您通常不希望在浮点或Decimal 计算后无差别地向下舍入.如果您认为必须这样做,请在格式化之前明确这样做:

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