too long float

[J. Peng]

hello,

why this happened on my python?
3.8999999999999999

I wanted 3.9 but got 3.89................
How to avoid it? thanks.

this is my python version:
'2.3.4 (#1, Feb 6 2006, 10:38:46) \n[GCC 3.4.5 20051201 (Red Hat 3.4.5-2)]'

 

[Chris]

hello,

why this happened on my python?

3.8999999999999999

I wanted 3.9 but got 3.89................
How to avoid it? thanks.

this is my python version:

'2.3.4 (#1, Feb 6 2006, 10:38:46) \n[GCC 3.4.5 20051201 (Red Hat 3.4.5-2)]'

True

http://effbot.org/pyfaq/why-are-floating-point-calculations-so-inaccurate.htm

 

[Dennis Lee Bieber]

why this happened on my python?

3.8999999999999999

I wanted 3.9 but got 3.89................
How to avoid it? thanks.

Avoid it? You don't... You alleviate the concern by understanding
that floating point is only precise if the value is a fraction of 2: 1,
0.5, 0.25, 0.125...

Computer Science recommends that one does NOT compare two floats for
equality -- instead one should compare the absolute value of the
difference of the two floats against some required epsilon (ie, how far
apart two floats can be and still be considered equal...
abs(f1 - f2) < 0.000001
for example)
--
Wulfraed Dennis Lee Bieber KD6MOG
(e-mail address removed) (e-mail address removed)
HTTP://wlfraed.home.netcom.com/
(Bestiaria Support Staff: (e-mail address removed))
HTTP://www.bestiaria.com/

 

[J. Peng]

thanks all!

Avoid it? You don't... You alleviate the concern by understanding
that floating point is only precise if the value is a fraction of 2: 1,
0.5, 0.25, 0.125...

Computer Science recommends that one does NOT compare two floats for
equality -- instead one should compare the absolute value of the
difference of the two floats against some required epsilon (ie, how far
apart two floats can be and still be considered equal...
abs(f1 - f2) < 0.000001
for example)
--
Wulfraed Dennis Lee Bieber KD6MOG
(e-mail address removed) (e-mail address removed)
HTTP://wlfraed.home.netcom.com/
(Bestiaria Support Staff: (e-mail address removed))
HTTP://www.bestiaria.com/

 

[Bart Ogryczak]

hello,

why this happened on my python?

3.9

bart

 

[Albert van der Horst]

3.9

This has nothing to do with python.

Apparently you don't know the first thing about floating point
numbers. I suggest reading the wikipedia entry.
http://en.wikipedia/wiki/floating_point

Groetjes Albert

 

[Steve Holden]

This has nothing to do with python.

Apparently you don't know the first thing about floating point
numbers. I suggest reading the wikipedia entry.
http://en.wikipedia/wiki/floating_point

Don't think you are the first person to make this mistake, by the way.
Despite Albert's tone suggesting that *everybody* knows about floating
point this is a very common issue among new programmers.

regards
Steve

 

[Grant Edwards]

Don't think you are the first person to make this mistake, by the way.
Despite Albert's tone suggesting that *everybody* knows about floating
point this is a very common issue among new programmers.

And even among old programmers who've not used floating point
much.