列表錯誤后無類型

Question

我無法理解第二個函數引發的錯誤。 當我通過第二個功能進行編程時，我意識到print（x）給了我：[['Anna'，74.0]，['Bill'，65.0]，['Cal'，98.0]]無

由於沒有此限制，因此我無法遍歷該列表並將其設置為L。是什么原因引起的？ 這是其他3個功能的粘貼框。 代碼在這里！ 。 任何建議或朝正確方向的推動都將不勝感激。

---

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)       

我對最后一個函數的預期代碼是：

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

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

但是它說我找不到nonetype的len，為什么我的xa none type？

Answer 1

average_grade()不返回列表，而是僅打印並返回None