[Tutor] cases with single if and an else clause

[Manprit Singh]

I would continue my discussion on this topic regarding the function written
and the way it is implemented, So finally it is done this way :

def grades(glist, score):
    if score < 0 or score > 100:
        raise ValueError
    for ch, rg in glist:
        if score < rg:
            return ch

lst = [("F", 60),
       ("D", 70),
       ("C", 80),
       ("B", 90),
       ("A", 101)]

try:
    marks= int(input("Enter marks"))
    grade = grades(lst, marks)

except ValueError:
    print("Invalid Value Entered")

else:
    print(f'for {marks} marks the grade is {grade}')

My Next question is, in this particular scenario, where keeping the
variable lst (which contains grade Characters and marks limits) as global
and passing it as an argument to the function grades. So when this function
is called, a copy of lst is created and it is destroyed upon exit from
function.

As the variable lst serves no other purpose, why not keep this lst as a
local variable inside the function grades .
Need some light on it .

Regards
Manprit Singh





On Wed, Oct 6, 2021 at 5:02 PM Alan Gauld via Tutor <tutor at python.org>
wrote:

> On 06/10/2021 12:04, Manprit Singh wrote:
> > Dear Dennis Lee Bieber,
> >
> > I  saw your explanation about my question :
> > GRADES = [ (60, "F"),
> >            (70, "D"),
> >            (80, "C"),
> >            (90, "B"),
> >            (100, "A") ] #ordered list of breakpoints
> >
> > These were the grades you have used, There is a problem, See if the marks
> > are 60 That should not be classified as F .
>
> All you need to do is change the comparison from <= to <
> (You also need to change the 100 to 101 for an "A" grade.)
> Alternatively, change all the test values to the highest vale
> for the grade: 59,69,...100 and keep the <= test
>
> > The way i have implemented it given below:
> >
> > def grades(glist, score):
> >     if score < 0 or score > 100:
> >         raise ValueError
> >     for ch, rg in glist:
> >         if score in rg:
> >             return ch
> >
> > lst = [("F", range(0, 60)),
> >        ("D", range(60, 70)),
> >        ("C", range(70, 80)),
> >        ("B", range(80, 90)),
> >        ("A", range(90, 101))]
>
> But now there is much more work generating ranges and using
> the in operation which implicitly loops over the values.
> A simple comparison is much cheaper. Although your version
> does exit as soon as it finds the correct range which will
> compensate somewhat. But 5 comparisons should be cheaper than
> an average of 3 'in' checks over 10 values(60 for the first!)
> even though the 'in' is written in C.
>
> > try:
> >     marks= int(input("Enter marks"))
> >     grade = grades(lst, marks)
> >
> > except ValueError:
> >     print("Invalid Value Entered")
> >
> > else:
> >     print(f'for {marks} marks the grade is {grade}')
> >
> > Can I make such a  program without using range ?
>
> Just change the comparison operator in Dennis' example.
>
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.amazon.com/author/alan_gauld
> Follow my photo-blog on Flickr at:
> http://www.flickr.com/photos/alangauldphotos
>
>
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