what is this?

[Herbert Fritsch]

Hi,
I'm a real beginner with python and I don't really know if I will get it.
But here is one of my first exercises:

Python 2.3+ (#1, Sep 23 2003, 23:07:16)
[GCC 3.3.1 (SuSE Linux)] on linux2
Type "help", "copyright" , "credits" or "license" for more information.[color=blue][color=green][color=darkred]
>>> a = 3
>>> b = 4
>>> b / 2 + a[/color][/color][/color]
5[color=blue][color=green][color=darkred]
>>> b / (2.0 + a)[/color][/color][/color]
0.8000000000000 0004

There must be something wrong. I' running the new Suse 9.0.

Herbert

[Peter Otten]

Re: what is this?

Herbert Fritsch wrote:
[color=blue][color=green][color=darkred]
>>>> b / (2.0 + a)[/color][/color]
> 0.8000000000000 0004
>
> There must be something wrong. I' running the new Suse 9.0.[/color]

No :-)

That's the way *all* floating point operations work, nothing python-specific
here. See

http://www.python.org/doc/faq/general.html#why-are-floating-point-calculations-so-inaccurate

Peter

[Jay Dorsey]

Re: what is this?

Herbert Fritsch wrote:[color=blue][color=green][color=darkred]
>>>>a = 3
>>>>b = 4
>>>>b / 2 + a[/color][/color]
>
> 5
>[color=green][color=darkred]
>>>>b / (2.0 + a)[/color][/color]
>
> 0.8000000000000 0004
>
> There must be something wrong. I' running the new Suse 9.0.[/color]

Not really. Think of the order of operations in mathematics.
Multiplication and division are ranked higher than addition. Using
parentheses for grouping is higher (before) mulitplication and division.

First example:

4 / 2 + 3 yields 2 + 3 yields 5

Second:

4 / (2.0 + 3)

Python coerces the 3 into a floating point number, so lets write all
these as floating points:

4.0 / (2.0 + 3.0)

Order of operations says do the parentheses first:

4.0 / 5.0 yields 0.8000000000000 004

Theres a listing of Pythons order of operations somewhere in the
documentation on python.org (couldn't find it with a quick search).

:)