round() function strange behaviour

[Erik de Castro Lopo]

brobbins333 at shaw.ca wrote:
> 
> I knew your name was familiar! I'm reading your book right now.
> It's excellent.

Thanks :-).

> VB for one, returns a proper rounded result on these
> recalcitrant numbers. 

VB probably stores rounded floating point numbers as strings instead
of the normal binary representation. VB like most scripting style 
languages (ie non-stringly typed languages) often hides the 
representation of the its variables.

> I'd be willing to bet that C can do it as well,
> but you should know better than I.

Python as it is written in C, gets its behaviour directly from C. What 
you are seeing is actually the behaviour of C.

> The problem is that I am trying to use the return value of round() as
> the return value of another function, so using Print to tidy it uup
> really doesn't do me any good. Any suggestions?

My suggestion is that instead of rounding the number you convert it
to a string of the required precision:

	erikd at coltrane > python
	Python 2.1.2 (#1, Jan 18 2002, 18:05:45) 
	[GCC 2.95.4  (Debian prerelease)] on linux2
	Type "copyright", "credits" or "license" for more information.
	>>> x = 56.78923
	>>> x_as_string = "%.2f" % x
	>>> print x_as_string
	56.79

Just what you want. Remember however that if you want to operate on the
number using standard arithmetic you need to work on x rather than 
x_as_string.

Erik
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  Erik de Castro Lopo  nospam at mega-nerd.com (Yes it's valid)
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