怎么限制小数点,
比如说
>>> 5/6.
0.83333333333333337

我想就要0.83

On 7/9/06, linda. s <samrobertsmith at gmail.com> wrote:
> 怎么限制小数点,
> 比如说
> >>> 5/6.
> 0.83333333333333337
>
>>> "%.3f"%(5/6.0)
'0.833'

> 我想就要0.83
>
> _______________________________________________
> python-chinese
> Post: send python-chinese at lists.python.cn
> Subscribe: send subscribe to python-chinese-request at lists.python.cn
> Unsubscribe: send unsubscribe to  python-chinese-request at lists.python.cn
> Detail Info: http://python.cn/mailman/listinfo/python-chinese
>
>


-- 
"""Time is unimportant, only life important!
blogging  :  http://blog.zoomquiet.org/pyblosxom/
wiki enter:   http://wiki.woodpecker.org.cn/moin/ZoomQuiet
in douban:  http://www.douban.com/people/zoomq/
"""

变成string了,如果我还是想要float,但同时想限制小数点?

On 7/9/06, Zoom. Quiet <zoom.quiet at gmail.com> wrote:
> On 7/9/06, linda. s <samrobertsmith at gmail.com> wrote:
> > 怎么限制小数点,
> > 比如说
> > >>> 5/6.
> > 0.83333333333333337
> >
> >>> "%.3f"%(5/6.0)
> '0.833'
>
> > 我想就要0.83
> >
> > _______________________________________________
> > python-chinese
> > Post: send python-chinese at lists.python.cn
> > Subscribe: send subscribe to python-chinese-request at lists.python.cn
> > Unsubscribe: send unsubscribe to  python-chinese-request at lists.python.cn
> > Detail Info: http://python.cn/mailman/listinfo/python-chinese
> >
> >
>
>
> --
> """Time is unimportant, only life important!
> blogging  :  http://blog.zoomquiet.org/pyblosxom/
> wiki enter:   http://wiki.woodpecker.org.cn/moin/ZoomQuiet
> in douban:  http://www.douban.com/people/zoomq/
> """
>
> _______________________________________________
> python-chinese
> Post: send python-chinese at lists.python.cn
> Subscribe: send subscribe to python-chinese-request at lists.python.cn
> Unsubscribe: send unsubscribe to  python-chinese-request at lists.python.cn
> Detail Info: http://python.cn/mailman/listinfo/python-chinese
>
>

十进制数在python内部都是通过二进制数表达的，所以"不存在"0.833这样一个float数值：
>>> 0.833
0.83299999999999996
这就是python内部float所能表达的最接近0.833的值。

如果你一定需要0.833（我觉得绝大多数时候其实并没有这个需求），就不能使用内建的float，要用别的自定义类型。

On 7/9/06, linda. s <samrobertsmith at gmail.com> wrote:
>
> 变成string了,如果我还是想要float,但同时想限制小数点?
>
> On 7/9/06, Zoom. Quiet <zoom.quiet at gmail.com> wrote:
> > On 7/9/06, linda. s <samrobertsmith at gmail.com> wrote:
> > > 怎么限制小数点,
> > > 比如说
> > > >>> 5/6.
> > > 0.83333333333333337
> > >
> > >>> "%.3f"%(5/6.0)
> > '0.833'
> >
> > > 我想就要0.83
> > >
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.exoweb.net/pipermail/python-chinese/attachments/20060709/27219c5b/attachment.html

import decimal

On 7/9/06, swordsp <sparas2006 at gmail.com> wrote:
> 十进制数在python内部都是通过二进制数表达的，所以"不存在"0.833这样一个float数值：
> >>> 0.833
> 0.83299999999999996
> 这就是python内部float所能表达的最接近0.833的值。
>
> 如果你一定需要0.833（我觉得绝大多数时候其实并没有这个需求），就不能使用内建的float，要用别的自定义类型。
>
>
>  On 7/9/06, linda. s <samrobertsmith at gmail.com> wrote:
> > 变成string了,如果我还是想要float,但同时想限制小数点?
> >
> > On 7/9/06, Zoom. Quiet <zoom.quiet at gmail.com> wrote:
> > > On 7/9/06, linda. s <samrobertsmith at gmail.com > wrote:
> > > > 怎么限制小数点,
> > > > 比如说
> > > > >>> 5/6.
> > > > 0.83333333333333337
> > > >
> > > >>> "%.3f"%(5/6.0)
> > > '0.833'
> > >
> > > > 我想就要0.83
> > > >
> >
> >
>
> _______________________________________________
> python-chinese
> Post: send python-chinese at lists.python.cn
> Subscribe: send subscribe to
> python-chinese-request at lists.python.cn
> Unsubscribe: send unsubscribe to
> python-chinese-request at lists.python.cn
> Detail Info:
> http://python.cn/mailman/listinfo/python-chinese
>
>

引自shhgs的帖子"Py2.5 What's new 之 with" （搜索前贴能找到）
==================================================
...
decimal模块提供了一个能返回context对象的context_manager()方法(请注意看注释，
至少Py2.5b1里面是没有这个方法，你得用get_manager() )，这个context对象
(context是上下文的意思)将计算的精度和近似要求封装了起来
(什么叫上下文？这才叫上下文！Perl的那个上下文根本就是假冒伪劣):

import decimal

# Displays with default precision of 28 digits
v1 = decimal.Decimal('578')
print v1.sqrt()

ctx = decimal.Context(prec=16)
#----------------------------------------
# 根据shhgs的试验，ctx对象是没有context_manager()方法的，
# 你得
# with ctx.get_manager() :
#----------------------------------------
with ctx.context_manager():
   # All code in this block uses a precision of 16 digits.
   # The original context is restored on exiting the block.
   print v1.sqrt()
...
===========================================

On 7/9/06, shhgs <shhgs.efhilt at gmail.com> wrote:
>
> import decimal
>
> On 7/9/06, swordsp <sparas2006 at gmail.com> wrote:
> > 十进制数在python内部都是通过二进制数表达的，所以"不存在"0.833这样一个float数值：
> > >>> 0.833
> > 0.83299999999999996
> > 这就是python内部float所能表达的最接近0.833的值。
> >
> > 如果你一定需要0.833（我觉得绝大多数时候其实并没有这个需求），就不能使用内建的float，要用别的自定义类型。
> >
> >
> >  On 7/9/06, linda. s <samrobertsmith at gmail.com> wrote:
> > > 变成string了,如果我还是想要float,但同时想限制小数点?
> > >
> > > On 7/9/06, Zoom. Quiet <zoom.quiet at gmail.com> wrote:
> > > > On 7/9/06, linda. s <samrobertsmith at gmail.com > wrote:
> > > > > 怎么限制小数点,
> > > > > 比如说
> > > > > >>> 5/6.
> > > > > 0.83333333333333337
> > > > >
> > > > >>> "%.3f"%(5/6.0)
> > > > '0.833'
> > > >
> > > > > 我想就要0.83
> > > > >
> > >
> > >
> >
> > _______________________________________________
> > python-chinese
> > Post: send python-chinese at lists.python.cn
> > Subscribe: send subscribe to
> > python-chinese-request at lists.python.cn
> > Unsubscribe: send unsubscribe to
> > python-chinese-request at lists.python.cn
> > Detail Info:
> > http://python.cn/mailman/listinfo/python-chinese
> >
> >
>
> _______________________________________________
> python-chinese
> Post: send python-chinese at lists.python.cn
> Subscribe: send subscribe to python-chinese-request at lists.python.cn
> Unsubscribe: send unsubscribe to  python-chinese-request at lists.python.cn
> Detail Info: http://python.cn/mailman/listinfo/python-chinese
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.exoweb.net/pipermail/python-chinese/attachments/20060712/8ecb2c1f/attachment.html