float64 print digits

Peter Otten __peter__ at web.de
Fri Mar 2 12:15:10 CET 2007


Ulrich Dorda wrote:

[Warning: I'm no expert and don't have numpy installed]

> I need a pytho nscript to read numbers(with loads of digits) from a
> file, do some basic math on it and write the result out to another file.
> 
> My problem: I don't get python to use more digits:
> 
> In order to try this I type:
> 
> The normal precision one:
>  >>> from numpy import *
>  >>> x=1.23456789123456789123456789
>  >>> print "%35.25e" %x
>     1.2345678912345679000000000e+000
> 
> 
>     Now I try to use float64 to get more digits
> 
>  >>> z=zeros(3,float64)
>  >>> z[0]
> 0.0
>  >>> type(z[0])
> <type 'numpy.float64'>
>  >>> z[0]=1.23456789123456789123456789

The right side of the assignment is a float, so the extra digits would
already be lost before you get a chance to convert to float64. But then
Python's float is a C double and should already use 64 bits...


>  >>> type(z[0])
> <type 'numpy.float64'>
>  >>> print "%35.25e" %z[0]
>     1.2345678912345679000000000e+000
> 
> This cuts the digits just like the 32bit case.
> 
> Can anyone please help me get more digits?

gmpy?

Peter



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