Python 嵌套列表：如何将特定元素和 append 打印到每个子列表

Question

quizes = [["Andrew"], ["Amy"], ["Jared"], ["Bob"], ["Sarah"]]

for i in range(len(quizes)):
    grade = eval(input("Enter", quizes[i][0],"grade:"))
    quizes[i].append(grade)
    print(quizes[i])

Hey guys so I been working on this for the past week and can't solve this. I am trying to get my program to ask "Enter [person1] grade: " and so on and append a second element to each sublist which will be their grade and then print the contents of the entire list. Any help is appreciated

Answer 1

You need to change:

    grade = eval(input("Enter", quizes[i][0],"grade:"))

to

    grade = eval(input("Enter " + quizes[i][0] + " grade:"))

input does not behave as print does. You can't use commas to join text in any other function (except for a very small number of custom functions and modules), and you should stay away from them at if that's confusing for you to only use them sometimes.

With that change, does your code work now? You didn't tell us why it wasn't working the way you expected.

Answer 2

The main problem is that input() accepts only one argument as the input prompt, unlike print which can take any number of arguments - you're giving 3 parameters to the input function - "Enter" , quizes[i][0] , and "grade:" .

You can try concatenating them - like input("Enter "+str(quizes[i][0])+" grade:") (the str() conversion is not needed if you know that all the quizes[i][0] will be strings already), or even use string formatting - "Enter {} grade".format(quizes[i][0]) or f"Enter {quizes[i][0]} grade:"

This should be enough, but there are 2 more changes you can make to your code if you like -

• Iterate over the nested lists directly ( for sub_list in quizes: )
• Using int() or float() to convert a returned input string containing a number will also work in place of eval

For example

for quiz in quizes:
   grade = eval(input("Enter {} grade:".format(quiz[0])))
   quiz.append(grade)
   print(quiz)

EDIT: Python docs on string formatting The f"..." syntax works only for Python 3.6+

Answer 3

The problem is input takes 1 string as a parameter, you are passing 3 instead. So:

quizes = [["Andrew"], ["Amy"], ["Jared"], ["Bob"], ["Sarah"]]

for l in quizes:
    grade = eval(input(f"Enter {l[0]} grade:"))
    l.append(grade)
    print(l)

However, I respectfully don't understand the point of using eval here. Eval turns data into code. Using eval on user input creates a great security hole. In the above code, what if the user input quizes.clear() ? The whole array will be emptied. What if he inputs something eviler?

Consider (assumes valid grades only contain numbers):

quizes = [["Andrew"], ["Amy"], ["Jared"], ["Bob"], ["Sarah"]]

for l in quizes:
    while True:
        try:
            grade = float(input(f"Enter {l[0]} grade:"))
        except ValueError:
            print("Please input a number.")
        else:
            l.append(grade)
            break
print(quizes)

Answer 4

Now that I'm looking at it, what did yours do wrong?

quizes = [["Andrew"], ["Amy"], ["Jared"], ["Bob"], ["Sarah"]]

for quiz in quizes:
    grade = eval(input("Enter " + quiz[0] + " grade:"))
    quiz.append(grade)
    print(quiz)

print(quizes)