我不知道我的代码有什么问题（刚开始 python）

Question

i have made a list by using while list and then used if statements. In the first two conditions, the code runs perfectly without any error. But in the third condition it is showing that the list is empty. I have no clue what is wrong here.

CODE:

# time table generator with python

import random
no_of_classes = int(input("Please enter the number of classes in a day: "))
name_of_classes = input("Please enter the subject name/name of classes (please separate then by commas): ")
class_name_list = name_of_classes.split(",")
days_in_week = int(input("Enter the number of days in a week for which the school is working:"))
list_1 = [] `list with the problem`
x = 1
while x <= no_of_classes:
    list_1.append(x)
    x += 1

final_list = []
for j in range(days_in_week):
    subject_list = []
    if no_of_classes > len(class_name_list):
        for i in class_name_list:
            a = random.choice(list_1)
            subject_list.insert((a - 1), i)
        for m in range(no_of_classes - len(class_name_list)):
            b = random.choice(class_name_list)
            subject_list.append(b)
        final_list.append(subject_list)

    elif no_of_classes == len(class_name_list):
        for i in class_name_list:
            a = random.choice(list_1)
            subject_list.insert((a-1), i)
        final_list.append(subject_list)

    else:   `having problem with this condition`
        temp_class_list = []
        list_2 = class_name_list
        for m in range(no_of_classes):
            n = random.choice(list_2)
            a = random.choice(list_1)
            list_1.remove(a)
            list_2.remove(n)
            subject_list.insert((a-1), n)

for k in range(days_in_week):
    print(final_list[k])

OUTPUT:

Traceback (most recent call last):
  File "/Users/arungupta/Documents/trial (delete).py", line 24, in <module>
    a = random.choice(list_1)
  File "/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/random.py", line 301, in choice
    raise IndexError('Cannot choose from an empty sequence') from None
IndexError: Cannot choose from an empty sequence

THANK YOU FOR YOUR HELP. MUCH APPRECIATED!!!

Answer 1

You just forgot to fill the final_list: final_list.append(subject_list)

else:   
    temp_class_list = []
    list_2 = class_name_list
    for m in range(no_of_classes):
        n = random.choice(list_2)
        a = random.choice(list_1)
        list_1.remove(a)
        list_2.remove(n)
        subject_list.insert((a-1), n)
        final_list.append(subject_list)

Answer 2

There are two problems actually:

• You forgot final_list.append(subject_list) as noted by Castiell
• You emptied list_1 , which makes your program crash in the next iteration (and actually, the error message you showed is due to this)

Here is my proposed correction: make a copy of list_1 before you empty it:

    else:
        temp_class_list = []
        list_2_copy = class_name_list.copy()
        list_1_copy = list_1.copy()
        for m in range(no_of_classes):
            n = random.choice(list_2_copy)
            a = random.choice(list_1_copy)
            list_1_copy.remove(a)
            list_2_copy.remove(n)
            subject_list.insert((a-1), n)
        final_list.append(subject_list)

(I also made a copy of class_name_list because I suspect it is the source of another undiscovered bug)