There is definitely a secondary understanding of math that comes from working on computers. How computers do math is quite a bit different from how you or I do it on a piece of paper. The fact that python can do arbitrary large integer arithmetic makes it quite nice for many math applications as you don't have to deal with some of the issues of other languages.
Floating point numbers are different than anything you may have encountered out of computing. Their nuances are fully detailed in the wonderful "What every computer scientist should know about floating point": http://docs.sun.com/source/806-3568/ncg_goldberg.html However, the paper is a little long and quite obtuse, even though it goes through everything from a mathematical perspective. Don't feel like you need to understand it, but when you DO need to understand the true issues with floating point, that will be your guide. There is also great advantage in learning how to do fixed point calculations, especially in python, with its awesome integer type. This is especially the case for times when you need very accurate addition and subtraction, such as with large quantities of money. http://fixedpoint.sourceforge.net/ is a project that implements it. I don't seem to see fixed point numbers in the python standard libraries, but then again, I'd not be surprised if they were there. --Michael -- Michael Langford Phone: 404-386-0495 Consulting: http://www.TierOneDesign.com/ Entertaining: http://www.ThisIsYourCruiseDirectorSpeaking.com On 9/18/07, Ian Witham <[EMAIL PROTECTED]> wrote: > > As Michael points out, you need to explicitly use the round function, as > the float formatting merely truncates anything after the second decimal > place. > > I ran across a similar problem with the int() fuction early on. Anything > after the decimal point is truncated, not rounded, leading to behavior I was > not expecting. > > For example: > > int(-1.5) == -1 > int(-.5) == 0 > int(.5) == 0 > int(1.5) == 1 > > Ian > > > On 9/19/07, Christopher Spears < [EMAIL PROTECTED]> wrote: > > > > I wrote a script that takes a price and a sales tax > > and calculates the new price. > > > > #!/usr/bin/env python > > > > def calculate_price(price, percent_tax): > > sales_tax = price * percent_tax > > new_price = price + sales_tax > > return new_price > > > > price = float(raw_input("Enter a price: ")) > > percent_tax = float(raw_input("Enter a sales tax: ")) > > print "%.2f" % calculate_price(price, percent_tax) > > > > Here is the script in action: > > [EMAIL PROTECTED] ./chap5 173> python sales_tax.py > > Enter a price: 10.00 > > Enter a sales tax: .0825 > > 10.82 > > > > I'm not convinced that the new price is completely > > accurate because the price without the string > > formating is 10.825 > > > > [EMAIL PROTECTED] ./chap5 164> python sales_tax.py > > Enter a price: 10 > > Enter a sales tax: .0825 > > 10.825000 > > > > Wouldn't the price be rounded up to 10.83 in the real > > world? How can I accomplish this? > > _______________________________________________ > > Tutor maillist - Tutor@python.org > > http://mail.python.org/mailman/listinfo/tutor > > > > > _______________________________________________ > Tutor maillist - Tutor@python.org > http://mail.python.org/mailman/listinfo/tutor > >
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