Rounding Bug in Python 2.0! - ugh

[Pete Forman]

hzhu at users.sourceforge.net (Huaiyu Zhu) writes:

> On 01 Nov 2000 14:39:05 +0000, Pete Forman <gsez020 at kryten.bedford.waii.com>
> wrote: 
> >
> >It would be nice if Python would make use of dtoa() rather than
> >stock sprintf() to display floating-point numbers.  There are
> >variants of dtoa in netlib and libg++.
> 
> Some simple examples of what dtoa do differently?

The gateway from the mailing list to Usenet is (still?) broken, so
I'll repeat an example I mailed earlier.

IEC 60559           Full precision      Desired display
---------           --------------      ---------------
0x4008fbe76c8b4395  3.1229999999999998  3.1229999999999998
0x4008fbe76c8b4396  3.1230000000000002  3.123
0x4008fbe76c8b4397  3.1230000000000007  3.1230000000000007


The criteria that I'm looking to satisfy are:

  1) Round trip - reading a written number should give the same result
  2) Write the minimum number of digits - drop trailing zeros/nines

-- 
Pete Forman                 -./\.- Disclaimer: This post is originated
Western Geophysical           -./\.-  by myself and does not represent
pete.forman at westgeo.com         -./\.-  the opinion of Baker Hughes or
http://www.crosswinds.net/~petef  -./\.-  its divisions.