On Wed, Jul 28, 2010 at 6:11 AM, Evert Rol <evert....@gmail.com> wrote: > Sorry, forgot to reply-to-all: > > > I don't know the book nor the exercise, but see my comments interspersed in > the code, and a few general remarks at the bottom > >> From a practice exercise in Building Skills In Python page 64 I'm >> working on How Much Does The Atmosphere Weigh? Part 1: >> To check it states that the answer should be app. 10**18kg However, >> and I've checked to make sure that the math I've layed out matches up >> with the texts, I get 5.07360705863e+20 >> >> In the code I have broken the order of operations down to more >> parenthetical, and tried outright, but see nothing obvious about how >> it's strung together. If anyone has had a similar experience with the >> problem given, or see anything blatantly obvious I've done wrong with >> the ordering of operations. I tried to include as much of the >> problem(formulas are just above variables they're used in) as comments >> as possible. >> >> import math >> def atmosphereWeight(): >> pi = math.pi >> """Air Pressure (at sea level) P0. This is the long-term average. >> P0 = 1.01325 × 10**5""" >> airPressCLevl = 1.01325*(10**5) >> gravity = 9.82 >> """We can use g to get the kg of mass from the force of air >> pressure P0. Apply the acceleration of gravity >> (in m/sec2) to the air pressure (in kg · m/sec2). This result is >> mass of the atmosphere in kilograms per >> square meter (kg/m2). >> Mm2 = P0 × g""" >> masAtmoInKgPerSqM = airPressCLevl * gravity > > Simply from looking at the units left and right of the equality sign, you'll > need to *divide* by g, not multiply: [kg] = [kg m / s^2] / [m / s^2] > > >> """Given the mass of air per square meter, we need to know how >> many square meters of surface to apply >> this mass to. Radius of Earth R in meters, m. This is an average >> radius; our planet isn’t a perfect sphere. >> R = 6.37 × 10""" >> avgRadiusEarth = 6.37 * (10**6) >> """The area of a Sphere. >> A = 4πr2""" >> areaSphere = 4 * pi * (avgRadiusEarth**2) >> """Mass of atmosphere (in Kg) is the weight per square meter, >> times the number of square meters >> Ma = P0 × g × A""" >> masEarthAtmoInKgPerSqM = airPressCLevl * gravity * areaSphere > > ditto here: divide by gravity, not multiply by it. > > >> print(masEarthAtmoInKgPerSqM) >> >> atmosphereWeight() > > > Few general remarks: > - the standard way of writing numbers with a power of ten in code is > something like 1.01325e5. I guess this is also easier/quicker to execute (not > that this code is time-critical, but in general)
I'll probably ending up reading something about it later in the book, but as a quick question, why does: >>> 5e18 == 5**18 False >>> int(5e18) == int(5**18) False >>> 1.01325e5 == 1.01325**5 False > - why do you assign masTmoInKgPerSqM, then later not use it when calculating > masEarthAtmoInKgPerSqM? I turned all of the formulas given into a variables, however in masEarthAtmoInKgPerSqM it would have been neater to use masTmoInKgPerSqM * areaSphere, instead of reusing the two variables again in .masEarthAtmoInKgPerSqM. > - just use math.pi when calculating areaSphere, instead of "pi = math.pi" and > then later using pi. For me, that's just as clear. > - no need to put parentheses around powers; they are evaluated before the > multiplication (unless this is what you meant by "to more parenthetical" Yes, it was just to break it into smaller, more readable, pieces. > - try indenting the comments as well; more readable It looked better when color coded in the editor, but not here in black and white. > > Probably not all of the above are necessary, if you wrote this for debugging > your problem, but they're just some thoughts that occurred to me. > > Enjoy your calculations. Will the 'fun' never end? > _______________________________________________ > Tutor maillist - tu...@python.org > To unsubscribe or change subscription options: > http://mail.python.org/mailman/listinfo/tutor > _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
