Using the following dictionary, create a program that takes an argument (subject) and prints the average score excluding that subject, to two decimals.

grades = {'Biology':80, 'Physics':88, 'Chemistry':98, 'Math':89, 'English':79, 'Music':67, 'History':68, 'Art':53, 'Economics':95, 'Psychology':88}

For example:

• If the argument is Biology, it should print 80.56
• If the argument is Chemistry, it should print 78.56

Below what I've tried so far:

import sys

grades = {'Biology':80, 'Physics':88, 'Chemistry':98, 'Math':89, 'English':79, 'Music':67, 'History':68, 'Art':53, 'Economics':95, 'Psychology':88}

def average_grade():
    key = sys.argv[1]
    included_keys = grades.pop(key)

    average = sum(included_keys)/len(included_keys)
    return round(average, 2)

average_grade()

CodePudding user response：

This will work. I just deleted the specific subject from the dictionary with a del statement, then I get all the values with grades.values() and I get the number of grades left with len(grades).

import sys

grades = {'Biology':80, 'Physics':88, 'Chemistry':98, 'Math':89, 'English':79, 'Music':67, 'History':68, 'Art':53, 'Economics':95, 'Psychology':88}

def average_grade():
    key = sys.argv[1]
    del grades[key]
    average = sum(grades.values())/len(grades)
    return round(average, 2)

print(average_grade())

• py file.py Biology it outputs 80.56
• py file.py Chemistry it outputs 78.56

Of course it would be best to use some sort of error checking as well.

For example:

def average_grade():
    key = sys.argv[1]
    if key not in grades:
        return "Subject does not exist. Please try again."
    del grades[key]
    average = sum(grades.values())/len(grades)
    return round(average, 2)

if __name__ == "__main__":
    print(average_grade())

Now if I enter py file.py German it outputs Subject does not exist. Please try again.

CodePudding user response：

I would suggest using a copy of the dictionary, so the original dictionary will remain the same.

grades = {'Biology':80, 'Physics':88, 'Chemistry':98, 'Math':89, 'English':79, 'Music':67, 'History':68, 'Art':53, 'Economics':95, 'Psychology':88}

def average_grade(key):
    g = grades.copy()
    try:
        g.pop(key)
    except KeyError:
        print('Subject not exixts')
        return None

    average = sum(g)/len(g)
    return round(average, 2)

print(average_grade())

In your code included_keys = grades.pop(key) will return a number not a list and the calculation goes wrong here average = sum(included_keys)/len(included_keys)

CodePudding user response：

Use a generator expression to skip the unwanted key, and statistics.mean to calculate the mean.

from statistics import mean

def average_grade(grades, exclude):
    if exclude in grades:
        return mean(v for k, v in grades.items() 
            if k != exclude)
    raise KeyError(f'Subject "{exclude}" not found')

average = average_grade(grades, sys.argv[1])
print(f"{average:.2f}")