On 01/25/2014 10:01 PM, Keith Winston wrote:
On Sat, Jan 25, 2014 at 3:57 AM, spir <denis.s...@gmail.com> wrote:
.009 to the price, so that people do not have to type the full amount.
Example, 3.49 /gallon would return 3.499 /gallon.
This is what I have tried and the results of it.
def gas_price(price):
price == raw_input("What is the price of gas?") return price + .09
3.49=> 3.4899999999999998
I think there's an inconsistency in your post that might confuse the
answers. You mention in the lead that you want to add 9 ONE HUNDREDTHS
of a dollar, or tenths of a cent (which is in fact how gas is priced
in the US, and yes it's crazy stupid). However in your example you add
only tenths, but then in the answer you appear to have added
hundredths, which makes me think that you didn't cut & paste, but
rather retyped (and mistyped).
This will make it a little trickier to use Denis' last idea of using
integers, since you'll have to take them out one more order of
magnitude.
I guess this is what I wrote (unit was 1/10 cent), or maybe I misunderstand your
point.
If this exercise is later followed by interest
calculations, or anything like that, you might regret limiting your
internal accuracy/representation.
I think that you should probably do your math in floating point (why
get complicated? And you might need the accuracy, for hundredths of
dollars and interest) and then format the output to be what you want.
Watch out for rounding.
p = 3.499
print('{0:.3f}'.format(p)) # format a float with 3 places after the decimal
3.499
p = 3.4994
print('{0:.3f}'.format(p))
3.499
p = 3.4999999
print('{0:.3f}'.format(p))
3.500
Yes; but this only corrects output, fo the user's comfort. If you need to do
further computations, then the internal representation must also be right (else
you'll get at best rounding errors, at worst worse ;-), and this can only be
ensured by computing on integers or decimals. Typically, using integers, you'll
choose a unit a few orders of magnitude lower than the most precise numbers
possibly involved in computations (eg, a tax rate of 0.1234567 ;-).
d
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