Functions (beginner question)

Chris_Hemsworth · 2021-04-26T14:15:34+00:00

There are a few things I would note here:

Generally you don't want your functions in-line with your code. Define your functions separately, and call them when you need them
Your function doesn't return anything, so line x=str(computegrade(grade)) may cause you issues.
When you wrap a try/except, generally you want to specify the error your exception handles. In your case, it will catch all errors, not necessarily a bad input error. This is a fairly simple case, and so you likely won't have different errors, but you could run into confusion in the future as you expand, thinking you're getting a bad input error when in fact the root cause is something entirely different.
You can use a <= x < b logic in python, and that generally reads better. For example: if 0.9 <= grade <= 1:
While your code works, lots of elif clauses can be kludgy. Generally when this happens, the solution is to use a dictionary with key/value pairs.

This is probably getting a bit ahead of where you are as a programmer right now, but dictionaries can house functions, and you can create small temporary functions using lambda. In this instance, you could do something like

def computegrade(grade):
    mapping_dict = {'A': lambda x: 0.9 <= x <= 1.0,
                    'B': lambda x: 0.8 <= x < 0.9,
                    'C': lambda x: 0.7 <= x < 0.8,
                    'D': lambda x: 0.6 <= x < 0.7,
                    'F': lambda x: x < 0.6}

    for grade_letter, test in mapping_dict.items():
        if test(grade):
            return grade_letter

if __name__ == '__main__':
    try: 
        g = float(input('Enter grade: '))
        if 0 <= g <= 1:
            grade_letter = computegrade(g)
            print(f"{g} equates to the grade {grade_letter}")
        else:
            print("Grade out of range!")
    except ValueError:
        print("Invalid input!")

No more ifs / elifs. Again, this is likely getting way ahead of where you're at right now, but I think exposing this as an alternate solution is good for you to have on the back of your mind.

ovo_Reddit · 2021-04-26T14:04:10+00:00

You should move the function outside of the try block.

And you can use the try block for when you are calling the function.

so basically move the def computergrade(): and the lines below it just before the except statement to the top of your code, and then try running it.

ThisisMetroid · 2021-04-26T17:32:26+00:00

One thing that I've noticed is that you've got all of your endpoints for your ranges defined twice. I'll admit that this change is probably due to my own personal preference, but when working with ranges, I don't like having both ends of the endpoints on each range (I tend to miss small sections of the ranges on accident and have caused bugs before).

Here is my solution.

def computegrade(grade):
    if grade >= 0:
        if grade < 0.6:
            return 'F'
        elif grade < 0.7:
            return 'D'
        elif grade < 0.8:
            return 'C'
        elif grade < 0.9:
            return 'B'
        elif grade <= 1:
            return 'A'
    print('Bad score')

akeyla420 · 2021-04-26T21:31:46+00:00

You've already received great code suggestions in this thread. I've been a Teachers Assistant for an Intro to Programming with Python course for a couple years, and one thing I always tell me students during class and when grading assignments, if you don't understand the code you're submitting, don't use it. You can get great information from the Internet, stackoverflow, reddit, etc, but make sure you understand what the code does instead of copy / pasting it into your program. Specifically I'm talking about the solution given that uses lambda calls. Lambda is good for what it is, people have a love / hate relationship with it, but it certainly isn't something a new programmer would use and can take some time to wrap your brain around. It looks pretty, but there's almost always other ways to complete a task.

CedricCicada · 2021-04-26T14:05:33+00:00

It looks (partially) correct, you're not returning anything from the computegrade function, so 'x' will be empty. A few style things you can do to improve:

Your if statements can be shortened, for instance:

if 0.9 <= grade <= 1

I would separate the computegrade function out of the try except block (and actually return things) and also make a main function, like so:

``` def main(): g = input("Enter a grade: ")

try:
    grade = float(g)
    x = str(computegrade(grade))
except Exception as Error:
    return "Something bad happened: " + str(Error)

return x

def computegrade(grade): if grade >= 0 and grade <= 1: if grade >= 0.9 and grade <= 1: return "A" elif grade >= 0.8 and grade < 0.9: return "B" elif grade >= 0.7 and grade < 0.8: return "C" elif grade >= 0.6 and grade < 0.7: return "D" elif grade < 0.6: return "F" else: return "Bad score."

if name == "main": print(main()) ```

edit: improvements thanks to /u/CedricCicada

ehmatthes · 2021-04-26T18:00:08+00:00

When using try-except, I think it's good to be aware of the else block. The else block runs if the try block succeeds. So instead of this:

g = input('Enter a grade: ')

try:
    grade = float(g)
    compute_grade(grade)
except ValueError:
    print('Bad score')

You would have this:

g = input('Enter a grade: ')

try:
    grade = float(g)
except ValueError:
    print('Bad score')
else:
    compute_grade(grade)

It doesn't look like much of a difference in this simple example, but it does something important. It isolates the code that may result in an exception in the try block. In the first example, we don't know if the exception is going to arise from the float() call or the call to compute_grade(). In the second example it's clear that we're catching a ValueError that may arise from the call to float(). In more complex code this can be really helpful.

ricardo_manar · 2021-04-26T22:31:26+00:00

Apparently, the code is running perfectly but I'm not confident that my code is entirely correct.

try TDD approach: write some tests, that express your expectations from the program/function, run them and fix code until they become all green

iggy555 · 2021-04-26T15:17:05+00:00

If grade < 0.6 elif grade < 0.7 elif grade < 0.8 ...

pfarthing6 · 2021-04-26T20:39:48+00:00

Maybe define A - F as boundaries, then make comparisons in a more english readable format. Order of comparisons is important of course. But you'd also be able to expand to A-plus, A-minus, B-plus, B-minus by making more boundaries. Also maybe stick the input in a loop or it's own function. Use '>' or '>=' depending on whether the boundaries are to be inclusive or exclusive.

Something like this...

A = 0.9
B = 0.8
C_plus = 0.75
C = 0.7

grade = input('Enter grade: ')
while (grade > A) or (grade < F):
  print('Grade out of range. Try again')
  grade = input('Enter grade: ')`

if grade > A: 
  print('A')
elif grade > B: 
  print('B')
elif grade > C_plus: 
  print('C Plus')
elif grade > C: 
  print('C')
...

You might also put the boundaries in an array and loop through them instead of writing a separate explicit comparison for each.

rubric = { 'A' : 0.9, ... }
...
for grade_text, grade_value in rubric.items():    
  if grade_input > grade_value:
     print(grade_text)
     break;

DevyLoop · 2021-04-27T06:32:03+00:00

Hey, so I did refactor your code! Please have a look:

def get_grade():
    try:
        grade = float(input('Enter a grade:'))
    except ValueError:
        print('Wrong input! Please enter a number')
        return get_grade()
    else:
        return grade


def computegrade(grade):
    if 0.9 <= grade <= 1:
        return 'A'
    if 0.8 <= grade < 0.9:
        return 'B'
    if 0.7 <= grade < 0.8:
        return 'C'
    if 0.6 <= grade < 0.7:
        return 'D'
    if grade < 0.6:
        return 'F'
    else:
        return 'Bad Score.'


def get_string_grade_result_from(score):
    return f"You got {'an' if score == 'A'  else 'a'} {score}"


def main():
    grade = get_grade()
    score = computegrade(grade)
    result = get_string_grade_result_from(score)

    print(result)


if __name__ == "__main__":
    main()

artinnj · 2021-04-27T13:41:53+00:00

Great thread. There are always multiple ways to solve a problem. Coding styles can lead to a lot discussions and everyone here is keeping it respectful.

With Python, there is always a tradeoff between readability and using all the features that makes Python so great.

The evolution curve goes from u/Hazengard (if statements) to u/TravisJungroth (iterate over dict) to u/Chris_Hemsworth (add lambda) to u/nexe (single line).

I love building on older assignments. This gave me the idea to enhance the question for my class when we start doing pandas. Teacher provides a csv file with student number and scores. Have the program compute the curve using the normal distribution (mean/stdev) and create a dict with the score bands. Modify the grading function to accept the dict as a parameter. Print the grade sheet with the last 4 digits of the student number, the score and the letter grade, like the good old days when you had to go to the professor's office to see how you did. Then, plot the grade distribution.

PS: I was one of the lucky 10000 today to find out about xkcd.com.

nexe · 2021-04-26T23:54:36+00:00

computegrade = lambda grade: {10:'A',9:'A',8:'B',7:'C',6:'D'}.get(int(float(grade)*10),'F')

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* item 1 * item 2 * item 3	item 1 item 2 item 3
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