Alan Gauld wrote:
"David" <da...@abbottdavid.com> wrote
I took this program that determines a fertilizer application rate;
...
And converted it to class/object to learn how they work. Just looking
for some pointers, if I did it correctly etc.
For such a small program its hard to see what else you could have done.
Technically itys not too bad, I've made a couple of suggestions below.
However, leaving the fact that its an excercise I'd say that really this
is just a function rather than a class.
class FertRate:
def __init__(self, rate, nitrogen, acre, bag):
self.area = 43.560
self.app = rate / (nitrogen / 100.00)
self.acre = acre
self.bag = bag
def result(self):
result = self.app * self.area * self.acre / self.bag
print 'You should apply %0.2f bags.' % result
Its never a good idea to include printing in the same function as
calculation. IT would be better to have two functions one to calculate
and one to generate the printable output. (The actual printing is best
done outside the class altogether, it improves the reusability. For
example prints don't work in a GUI but a formatted string can be used.
But even if you keep it as one function at lest return the result as a
string rather than print it
def main():
rate, nitrogen, acre, bag = get_inputs()
frate = FertRate(rate, nitrogen, acre, bag)
This could have just been:
frate = FertRate( get_inputs() )
which saves the need for the variables.
frate.result()
So if you took my advice about returning a string this becomes
print frate.result()
But as I say you could just have made FertRate a function:
print FertRate( get_inputs() )
and it would have been just as effective, classes really only start to
be useful on slightly larger programs than this.
But as an example of using a class its nearly OK, just the tweak of the
return value to think about - and that applies to the function version too!
Thanks Alan,
this works;
def main():
rate, nitrogen, acre, bag = get_inputs()
frate = FertRate(rate, nitrogen, acre, bag)
result = frate.result()
print 'You should apply %0.2f bags.' % result
but I get an error here;
def main():
frate = FertRate(get_inputs())
result = frate.result()
print 'You should apply %0.2f bags.' % result
Traceback (most recent call last):
File "./fert_class.py", line 26, in <module>
main()
File "./fert_class.py", line 15, in main
frate = FertRate(get_inputs())
TypeError: __init__() takes exactly 5 arguments (2 given)
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