是Python的新手。.GradepointAVG？

Question

Rather than asking the user to enter a number, modify gpa.py to enter 5 grades, but make it letter grades (A, A-, B+, etc). Please input these grades, convert them to 4 point scale equivalents, (a=4.0, a- = 3.7, B+ =3.3, B= 3.0, B- = 2.7, C+ =2.3, C = 2.0, C- =1.7 etc.). Print out the numeric equivalent of the average of these 5 grades.

originally for the first program i did i had

print("This program calculates grade point average.")
g1 = float(input("Enter course 1 grade -> "))
g2 = float(input("Enter course 2 grade -> "))
g3 = float(input("Enter course 3 grade -> "))
g4 = float(input("Enter course 4 grade -> "))
g5 = float(input("Enter course 5 grade -> "))
sum = g1 + g2 + g3 + g4 + g5
count = 5
print ("Your GPA for last semester was -> ", sum / count)

but after reading this it tells me it wants me to assign grades, so i made it this

print("This program calculates grade point average.")
g1 = a
g2 = b
g3 = c
g4 = c+
g5 = b-
sum = g1 + g2 + g3 + g4 + g5
count = 5
print ("Your GPA for last semester was -> ", sum / count)

how can i make the grades from strings to ints and then give the grade point average?

Answer 1

You can use a dict to lookup numeric values based on the input string

>>> grades = {'A':4.0, 'A-':3.7, 'B+':3.3, 'B':3.0 ... etc}
>>> grades['B']
3.0

Answer 2

Your method is a long of way of accomplishing the task. Use dictionaries like the user above has demonstrated. They can grow and decrease in size and will be much easier storing large amounts of data.

Answer 3

You can use a dict as suggested to map note letters to their numerical equivalent. Do not forget to surround it with a try in case of a wrong grade is given (ie Z).
Also, it is way more readable to use lists and loops instead of repeating the same code.

# Grades dictionnary
letter_grades = {
    'A' : 4.0,
    'A-' : 3.7, 
    'B+' : 3.3, 
    'B' : 3.0, 
    'B-' : 2.7, 
    'C+' : 2.3, 
    'C' : 2.0, 
    'C-' : 1.7,
    # and so on...
}

# Total grades
grades_number = 3
# List of grades
grades = []

print("This program calculates grade point average.")
for i in range(grades_number):
    grade = input("Enter course {} grade -> ".format(i+1))
    grades.append(grade)

try:
    # We try to sum the grades, but if a given one is wrong, then a KeyError with be thrown
    sum = sum([letter_grades[i] for i in grades])
    print ("Your GPA for last semester was -> ", sum / len(grades))
except KeyError:
    print("You entered a wrong grade.")

Answer 4

I have gotten it to work!

grades = {
'A':4.0,
'A-':3.7,
'B+':3.3,
'B':3.0,
'B-':2.7,
'C+':2.3,
'C':2.0,
'C-':1.7,
'D+':1.3,
'D':1.0,
'D-':0.7,
'F':0.0
}

print("This program calculates grade point average.")


g1 = grades['C']
g2 = grades['A']
g3 = grades['F']
g4 = grades['B-']
g5 = grades['D+']
total = g1 + g2 + g3 + g4 + g5
totalgrades = 5
print ("Your GPA for last semester was -> ", total / totalgrades)

Adding a dictionary helped the most. But I came to a point where i was getting an error at the 20th line(g1 = grades['A']) I had not put the grades part before ['A'] and thats what was wrong with it. all works now and good to go. Thank you everyone for the help.