Re: [Tutor] python precision output?
Andre Walker-Loud wrote: > To reiterate, I need str(value) to be written to my file with 16 > digits of precision...??? You can use string formatting to specify exactly how many decimal places to include: In [1]: v=1.0/7 In [2]: v Out[2]: 0.14285714285714285 In [3]: str(v) Out[3]: '0.142857142857' In [4]: '%.16f' % v Out[4]: '0.1428571428571428' Kent ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] python precision output?
> if you want accuracy and are willing to sacrifice the total range of > numbers that Python's IEEE754 double-precision floats give you, then > use the decimal.Decimal class instead -- better precision, smaller > range. > > however, if you wish to stick with floats, use the string format > operator and tell it you want 17 places after the decimal point: > x=7./13 x > 0.53846153846153844 str(x) > '0.538461538462' '%.17f' % x > '0.53846153846153844' > > hope this helps! This did the trick! thanks, Andre > -- wesley > - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - > "Core Python Programming", Prentice Hall, (c)2007,2001 > http://corepython.com > > wesley.j.chun :: wescpy-at-gmail.com > python training and technical consulting > cyberweb.consulting : silicon valley, ca > http://cyberwebconsulting.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] python precision output?
> The problem I am having is getting python to write number into this > input file, keeping 16 digits of precision. I have played around > interactively, and see that python default prints 17 digits of > precision to the screen, but when I use a replace command to write > into the input file, it only prints 12 digits of precision. The > relevant snipit of my script is >: > To reiterate, I need str(value) to be written to my file with 16 > digits of precision...??? if you want accuracy and are willing to sacrifice the total range of numbers that Python's IEEE754 double-precision floats give you, then use the decimal.Decimal class instead -- better precision, smaller range. however, if you wish to stick with floats, use the string format operator and tell it you want 17 places after the decimal point: >>> x=7./13 >>> x 0.53846153846153844 >>> str(x) '0.538461538462' >>> '%.17f' % x '0.53846153846153844' hope this helps! -- wesley - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - "Core Python Programming", Prentice Hall, (c)2007,2001 http://corepython.com wesley.j.chun :: wescpy-at-gmail.com python training and technical consulting cyberweb.consulting : silicon valley, ca http://cyberwebconsulting.com ___ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] python precision output?
Andre Walker-Loud wrote:
> Hi there,
>
Hi Andre,
First of all, please don't start a new thread by replying to an existing
thread, RFC compliant email readers will thread your post along with the
original posting based on headers other than the Subject. :-)
I don't think you'll ever get satisfactory precision using binary
floating point (the default for python's float type). Take a look at
the decimal module, I believe it will give you much better results for
your requirements.
Here is the module documentation:
http://docs.python.org/lib/module-decimal.html
And an example of it's usage:
>>> getcontext().prec = 6
>>> Decimal(1) / Decimal(7)
Decimal("0.142857")
>>> getcontext().prec = 28
>>> Decimal(1) / Decimal(7)
Decimal("0.1428571428571428571428571429")
Please post back if that doesn't help you out.
Sincerely,
e.
> I am using python to do some scripting. In particular, I am using it
> to run some jobs which require precision inputs. I do this by having
> python write an input file, which I then feed to some other program.
>
> The problem I am having is getting python to write number into this
> input file, keeping 16 digits of precision. I have played around
> interactively, and see that python default prints 17 digits of
> precision to the screen, but when I use a replace command to write
> into the input file, it only prints 12 digits of precision. The
> relevant snipit of my script is
>
> value = float( int(ai) * 6 * math.pi / (int(L)*int(T))
> replace = {'VALUE':str(value)}
> ini_file = open('generic_ini').read()
> f=open('my_input.xml','w')
> f.write(ini_file % replace)
> f.close()
>
> where, "ai", "L" and "T" are process dependent numbers defined in my
> script, and the output "my_input.xml", is just an xml file I later
> feed to another program, and this is why I replace 'VALUE' with a
> string.
>
> To reiterate, I need str(value) to be written to my file with 16
> digits of precision...???
>
>
> Thanks,
> Andre
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>
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[Tutor] python precision output?
Hi there,
I am using python to do some scripting. In particular, I am using it
to run some jobs which require precision inputs. I do this by having
python write an input file, which I then feed to some other program.
The problem I am having is getting python to write number into this
input file, keeping 16 digits of precision. I have played around
interactively, and see that python default prints 17 digits of
precision to the screen, but when I use a replace command to write
into the input file, it only prints 12 digits of precision. The
relevant snipit of my script is
value = float( int(ai) * 6 * math.pi / (int(L)*int(T))
replace = {'VALUE':str(value)}
ini_file = open('generic_ini').read()
f=open('my_input.xml','w')
f.write(ini_file % replace)
f.close()
where, "ai", "L" and "T" are process dependent numbers defined in my
script, and the output "my_input.xml", is just an xml file I later
feed to another program, and this is why I replace 'VALUE' with a
string.
To reiterate, I need str(value) to be written to my file with 16
digits of precision...???
Thanks,
Andre
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