weird multiplication behaviour in Python 2.5 under Kubuntu 8.10

[gedece]

My system:
 lsb_release -rd
Description: Ubuntu 8.10
Release: 8.10

apt-cache policy python
python:
  Instalados: 2.5.2-1ubuntu1
  Candidato: 2.5.2-1ubuntu1
  Tabla de versión:
 *** 2.5.2-1ubuntu1 0
        500 http://archive.ubuntu.com intrepid/main Packages
        100 /var/lib/dpkg/status

Under Kubuntu 8.10 updated from 8.04 I was trying a program in Python 2.5.2. I have this Python because adept doesn't show 2.6 or 3.0.

this program made a calculation and didn't meet the condition, so I begun testing it in the python command line. To my surprise I got this nice repeatable error.

Python 2.5.2 (r252:60911, Oct 5 2008, 19:24:49)
[GCC 4.3.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 2.15*7
15.049999999999999
>>>

clearly this should have read 15.05

[Florian Diesch (diesch)]

Thank you for taking the time to report this issue and helping to make Ubuntu better.

The reported behavior is a common problem when using floating point values: Due to the limited precision some values can't be expressed precisely, similar to e.g. 1/3 can't be expressed as a decimal value.

As this issue isn't really a bug I'm going to convert it to a question. Feel free to ask further questions if something about it isn't clear.