列表错误后的 NoneType

Question

我无法理解第二个函数引发的错误。当我破解第二个函数时，我意识到 print(x) 给了我： [['安娜'，74.0]，['比尔'，65.0]，['Cal'，98.0]] 无

由于这个无，我无法遍历列表并将其设置为 L。是什么导致了这个无？这是其他 3 个功能的粘贴箱。 code here!。非常感谢任何建议或朝着正确方向推动。

---

def string_avg(L):
'''(list of str) -> list of list
Given a list of strings where each string has the format:
'name, grade, grade, grade, ...' return a new list of 
lists where each inner list has the format :
[name (str), average grade (float)]
Requirement: This function should be 1 line long.

>>> string_avg(['Anna, 50, 92, 80', 'Bill, 60, 70', 'Cal, 98.5, 100, 95.5, 
98'])
[['Anna', 74.0], ['Bill', 65.0], ['Cal', 98.0]]
'''
return(average_grade((string_list(L))))


def string_avg_update(L):
'''(list of str) -> NoneType
Given a list of strings where each string has the format:
'name, grade, grade, grade, ...' update  the given 
list of strs to be a list of floats where each item 
is the average of the corresponding numbers in the 
string. Note this function does NOT RETURN the list.
>>> L = ['Anna, 50, 92, 80', 'Bill, 60, 70', 'Cal, 98.5, 100, 95.5, 98']
>>> string_avg_update(L)
>>> L 
[74.0, 65.0, 98.0]
'''

x = string_avg(L)       

我对最后一个函数的预期代码是：

Say I changed the last function code to: 
x = string_avg(L)       

for i in range(0,len(x)):
    L[i] = x[i][1] 

但它说我找不到 len of nonetype，为什么我的 x 是 none 类型？

Answer 1

average_grade() 不返回列表，而只打印它并返回 None