Hello,
I've just wanted to check Python's abilities as a calculator and this
is what came out: 1.0 + 3.0 + 4.6
8.5999999999999996
Ehm, how could I get the intuitively 'correct' result of - say - 8.6?
;-)
best regards
Steffen 9 2509
Steffen Glückselig wrote: 1.0 + 3.0 + 4.6
8.5999999999999996
Ehm, how could I get the intuitively 'correct' result of - say - 8.6? ;-)
You may find annex B of the python tutorial an interesting read: http://docs.python.org/tut/node16.html
tiissa wrote: Steffen Glückselig wrote:
> 1.0 + 3.0 + 4.6 8.5999999999999996
Ehm, how could I get the intuitively 'correct' result of - say - 8.6? ;-)
You may find annex B of the python tutorial an interesting read: http://docs.python.org/tut/node16.html
Yes, the simplest way to get what you are expecting is probably:
py> print 1.0 + 3.0 + 4.6
8.6
The print statement calls str() instead of repr(). In many (most?)
cases, this will print out what you expect it to. But you should be
aware of floating-point representation issues, and you should definitely
read the reference above. If you really do need precise decimal
representation, you can use the 2.4 decimal.Decimal objects:
py> d.Decimal("1.0") + d.Decimal("3.0") + d.Decimal("4.6")
Decimal("8.6")
But if you just want a handy calculator, I'd go with print.
STeVe
"Steffen Glückselig" <us****@gungfu.de> writes: Hello,
I've just wanted to check Python's abilities as a calculator and this is what came out:
1.0 + 3.0 + 4.6
8.5999999999999996
Ehm, how could I get the intuitively 'correct' result of - say - 8.6? ;-)
This is as correct as your computer's FPU can made it :)
-- http://www.peter.dembinski.prv.pl
tiissa wrote: Steffen Glückselig wrote:
>1.0 + 3.0 + 4.6
8.5999999999999996
Ehm, how could I get the intuitively 'correct' result of - say - 8.6? ;-)
You may find annex B of the python tutorial an interesting read: http://docs.python.org/tut/node16.html
In addition to what you find in the above link, the round function can
be used.
p = 1 #digits of precision after decimal
a, b, c = 1.0, 3.05, 4.6
print round(a+b+c,p)
-> 8.6
You also have the option to use the print statements '%' operator to
format the output.
a, b, c = 1.0, 3.05, 4.6
print "%.1f"%(a+b+c)
-> 8.6
_Ron
If you want to do decimal arithmetic, use the decimal module which is
new in Python 2.4.
Python 2.4 (#1, Jan 22 2005, 20:45:18)
[GCC 3.3.3 20040412 (Red Hat Linux 3.3.3-7)] on linux2
Type "help", "copyright", "credits" or "license" for more information. from decimal import Decimal as D D("1.0") + D("3.0") + D("4.6")
Decimal("8.6")
when you write '4.6', you get a binary floating-point number which is
not equal to the decimal number 4.6. 4.6
4.5999999999999996 4.6 == D("4.6")
False
Jeff
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.6 (GNU/Linux)
iD8DBQFCh720Jd01MZaTXX0RAoZZAJ0Q3qngITn7Vs/7T6li2QZeGAbsYgCeJ3SJ
aLW5MCjK7lRPeC87PKRLEsA=
=eITH
-----END PGP SIGNATURE-----
"Steffen Glückselig" <us****@gungfu.de> wrote in message
news:11**********************@g14g2000cwa.googlegr oups.com... 1.0 + 3.0 + 4.6 8.5999999999999996
Ehm, how could I get the intuitively 'correct' result of - say - 8.6? str(1.0+4.6+3.0)
'8.6'
See Lib Ref 2, Builtin functs, repr() and str(), Lan Ref (or tutorial)
section on % formating, and probably a few FAQ entries.
Terry J. Reedy
Ron Adam wrote: tiissa wrote:
Steffen Glückselig wrote:
>>1.0 + 3.0 + 4.6
8.5999999999999996
Ehm, how could I get the intuitively 'correct' result of - say - 8.6? ;-)
You may find annex B of the python tutorial an interesting read: http://docs.python.org/tut/node16.html
In addition to what you find in the above link, the round function can be used.
p = 1 #digits of precision after decimal a, b, c = 1.0, 3.05, 4.6 print round(a+b+c,p)
-> 8.6
You also have the option to use the print statements '%' operator to format the output.
a, b, c = 1.0, 3.05, 4.6 print "%.1f"%(a+b+c)
-> 8.6
_Ron
Just to clarify this, It was pointed out to me that round() doesn't
resolve the problem of floating points, and I agree. (Thanks Fredrik) round(1.0+3.05+4.6,1)
8.5999999999999996
The print statement displays it as 8.6.
The only way to avoid the problem completely is by using an alternative
numeric system such as decimal.
What rounding and print formatting do is give you some control within
the specifications of your requirements. Print for display purposes,
and round to minimize errors to within the needed precision.
for y in range(1000000):
.... x += 1.6
.... x
1600001.6000213262
Eventually this could be significant.
for y in range(1000000):
.... x = round(x+1.6,1)
.... x
3200001.6000000001
Here the error has been kept to a minimum. In most cases, it isn't a
problem, but it is something to be aware of. It does matter in banking
and I beleive there are standard ways of dealing with it.
Cheers,
_Ron
So for using the python-interpreter as a simple calculator using
'print' seems to be the simplest and still exact way...
Thanks for clarification
Steffen This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
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