类型错误：字符串索引必须是整数而不是字符串 Python

Question

我定义了一个函数 get_class_average()，它有一个参数“students”。这个 students 是一个包含三个学生的列表：lloyd、alice 和 tyler，这些学生实际上是字典。get_average() 是一个计算平均值的函数，运行得很好。当我尝试调用 get_class_average() 函数时，出现了错误：

typeerror string indices must be integers not str

我的代码

lloyd = {
    "name": "Lloyd",
    "homework": [90.0, 97.0, 75.0, 92.0],
    "quizzes": [88.0, 40.0, 94.0],
    "tests": [75.0, 90.0]
}
alice = {
    "name": "Alice",
    "homework": [100.0, 92.0, 98.0, 100.0],
    "quizzes": [82.0, 83.0, 91.0],
    "tests": [89.0, 97.0]
}
tyler = {
    "name": "Tyler",
    "homework": [0.0, 87.0, 75.0, 22.0],
    "quizzes": [0.0, 75.0, 78.0],
    "tests": [100.0, 100.0]
}

# Add your function below!
from math import *
def average(numbers):
    total = sum(numbers)
    total = float(total)
    ans = total / len(numbers)
    return ans
num = [1,2,4,5,6]
a = average(num)
print a

def get_average(student):
    homework = average(student["homework"])
    quizzes = average(student["quizzes"])
    tests = average(student["tests"])
    sum = (0.1*homework) + (0.3 * quizzes) + (0.6 * tests)
    return sum

student = [lloyd, alice, tyler]
for key in student:   
    a = get_average(key)
    print a

def get_letter_grade(score):
    if score >= 90:
        return "A"
    elif score >= 80:
        return "B"
    elif score >= 70:
        return "C"
    elif score >= 60:
        return "D"
    else:
        return "F"

avg = get_average(lloyd)
t = get_letter_grade(avg)
print t


def get_class_average(students):
    results = []
    students = [lloyd, alice, tyler]
    a= get_average(students)
    r= results.append(a)
    return r

student = [lloyd, alice, tyler]
for key in student:   
    a = get_class_average(key)

print a

Answer 1

你的 get_class_average() 函数应该接收整个学生列表，而不是一个一个学生。

把你的 for key in student: 循环去掉：

students = [lloyd, alice, tyler]
a = get_class_average(students)

在 get_class_average() 函数里，你似乎返回结果的时机不对；把 return 的缩进调整一下，让它不在循环里面。results.append() 返回的是 None，因为它是直接修改 results 的内容：

def get_class_average(students):
    results = []
    for key in students:   
        a= get_average(key)
        results.append(a)
    return results

不过这样还是不能计算整个班级的平均分；它只是把每个学生的平均分收集到一个列表里。