Python exercise: Calculates the minimum and maximum score for each student.

Question

total beginner to programming here, need your guidance.

I'm learning python from some free online course, then come across this particular exercise, which I already solved, but puzzling me having two different way produce different result. So here it goes..

The question: Using the text file studentdata.txt (shown below) write a program that calculates the minimum and maximum score for each student. Print out their name as well.

studentdata.txt:
joe 10 15 20 30 40
bill 23 16 19 22
sue 8 22 17 14 32 17 24 21 2 9 11 17
grace 12 28 21 45 26 10
john 14 32 25 16 89

My final attempt:

xFile = open("studentdata.txt", "r")

for xLine in xFile:
    xList = xLine.split()
    min = 100
    max = 0

    for x in xList[1:]:
        if int(x) > max:
            max = int(x)
    for x in xList[1:]:
        if int(x) < min:
            min = int(x)

print(xList[0],"\tmin: ",min,"\tmax: ",max)

xFile.close()

Result:

joe min: 10 max: 40
bill min: 16 max: 23
sue min: 2 max: 32
grace min: 10 max: 45
john min: 14 max: 89

Then I compared it to the given answer provided by the site (I rewrite it in my style):

xFile = open("studentdata.txt", "r")

for xLine in xFile:
    xList = xLine.split()
    print(xList[0],"\tmin: ",min(xList[1:]),"\tmax: ",max(xList[1:]))

xFile.close()

Which is more simple, but it produce slightly different (but vital) result:

joe min: 10 max: 40
bill min: 16 max: 23
sue min: 11 max: 9
grace min: 10 max: 45
john min: 14 max: 89

Notice that the result for sue is different. The 'automatic' version doesn't produce the right result. How this happened?

Thanks.

Answer 1

The problem with the second version is that it doesn't convert the scores to int before comparison. When comparing strings '32' comes before '9'.

You can fix the issue by converting the scores to int before using min and max:

with open("studentdata.txt", "r") as xFile:
    for xLine in xFile:
        xList = xLine.split()
        scores = [int(x) for x in xList[1:]]
        print(xList[0],"\tmin: ",min(scores),"\tmax: ",max(scores))

Answer 2

The answer which is provided on the site computes min and max taking lexicographical order in account. It's just a coincidence that rest of the answers match.

Answer 3

Try converting the input data to integers and it should work. Python has the simple "int()" method for that which you have already used in the first version. The thing is, that then comparing strings python uses alphabetical order. For example: "100000000" is less then "2". However int("100000000") is more then int("2") which solves the problem.

Answer 4

The second one compares them as strings, and strings are compared lexicographically by the first character of the string, for example '6' < '58' this is False, and this '8' > '234' is True.

Answer 5

This probably happened because in finding 'minimum' and 'maximum', the numbers are not converted to integer type, they are being taken as string type. You should first convert it using map function or other as per your convenience.

I did this and it worked-

print(xList[0],"\tmin: ",min(list(map(int, xList[1:]))),"\tmax: ",max(list(map(int, xList[1:]))))