如何重复获取用户的输入并跟踪它？

Question

I have a question about input loops and keeping track of it.

I need to make a program that will keep track of all the grades of a class. The thing is that the class size varies every semester, so there is no fixed number assigned to the number of students.

The program will stop taking input when a student enters a grade of -1.

while True:
    grade = int(input("Test: "))
    if grade < 0:
        break

How can I make it so that it keeps track of every single input?

Answer 1

You could use a list comp with iter and get the user to enter -1 to end the loop:

grades = [int(grade) for grade in iter(lambda:input("Enter grade or -1 to exit: "), "-1")]

iter takes a sentinel that will break the loop when entered, so as soon as the user enters -1 the loop will end.

When taking input and casting you should really use a try/except to validate what the users inputs:

grades = []
while True:
    try:
        grade = int(input(""Enter grade or -1 to exit: ""))
    except ValueError:
        # user entered bad input 
        # so print message and ask again
        print("Not a valid grade")
        continue
    if grade == -1:
        break
    grades.append(grade) # input was valid and not -1 so append it

Answer 2

grades = [] # initialize an empty list
while True:
    grade = int(input("Test: "))
    if grade < 0:
        break
    else:
        grades.append(grade) # add valid values to the list