获取“IndexError：无法从空序列中选择”并且不知道为什么我的序列为空

Question

这是完整的代码 该程序应该类似于秘密圣诞老人生成器。人 a 送了 x 件礼物，人 b 送了 y 件礼物，但他们没有得到自己的回报。 问题是我对python只有非常基本的经验，而且发生了这种情况。

import random
number_of_people=int(input("How many participants?"))
list_of_names=[]
list_of_numbers=[]
origional_list_to_use=[]
for i in range (number_of_people):
    name=input("What is the name of person "+str(i+1)+"?")
    number=int(input("How many is "+name+" giving?"))
    list_of_names.append(name)
    list_of_numbers.append(number)
    for i in range (number):
        origional_list_to_use.append(name)
list_to_use=origional_list_to_use
count=0
while count<number_of_people:
    giving=[]
    for i in range (list_of_numbers[count]):
        giving.append(random.choice(list_to_use))
    if list_of_names[count] not in giving:
         print(list_of_names[count]," gives to ",giving)
         count=count+1
         print(list_to_use)
         for giving in list_to_use:
             list_to_use.remove(giving)
    else:
         print("INVALID")
         count=0
         list_to_use=origional_list_to_use

给出一个错误，但为什么我的序列是空的？我在这里做错了什么？ 我认为它可能在我的列表中或使用随机？

抱歉，这里是完整的错误位。

Traceback (most recent call last):
  File "C:/Users/Name/Documents/Test.py", line 18, in <module>
    giving.append(random.choice(list_to_use))
  File "C:\Users\Name\AppData\Local\Programs\Python\Python38-32\lib\random.py", line 290, in choice
    raise IndexError('Cannot choose from an empty sequence') from None
IndexError: Cannot choose from an empty sequence

Answer 1

似乎有几个问题。我已经用下面的 cmets 解决了它们：

import random
number_of_people=3
list_of_names=[]
list_of_numbers=[]
origional_list_to_use=[]
for i in range (number_of_people):
    name=input("What is the name of person "+str(i+1)+"?")
    number=int(input("How many is "+name+" giving?"))
    list_of_names.append(name)
    list_of_numbers.append(number)
    for i in range (number):
        origional_list_to_use.append(name)

# prevent mutation of original_list_to_use by
# creating a copy instead of a reference
list_to_use=[*origional_list_to_use]
count=0
while count<number_of_people:
    # you use the name giving later in this block, you can't use that name here
    # giving = []
    giving_list = []
    for i in range (list_of_numbers[count]):
        giving_list.append(random.choice(list_to_use))
    if list_of_names[count] not in giving_list:
         # maybe not what you wanted?
         print(list_of_names[count]," gives to ", giving_list)
         count=count+1
         print(list_to_use)
         for giving in list_to_use:
             list_to_use.remove(giving)
    else:
         print("INVALID")
         count=0
         # do not mutate origional_list_to_use
         list_to_use=[*origional_list_to_use]

Answer 2

请阅读https://stackoverflow.com/help/mcve——它解释了如何在请求帮助时删除无关的细节。 当您让人们更容易帮助您时，答案的质量将会提高。

---

你抱怨这失败了：

list_to_use = []
random.choice(list_to_use)

当您为该函数提供零个元素可供选择时， 您将看到“无法从空序列中选择”IndexError。

要调试您的程序，您需要关注以下语句：

list_to_use.remove(giving)

注意这个循环：

for giving in list_to_use:
    list_to_use.remove(giving)

与分配空列表相同， 就像我上面做的那样。

---

或者，考虑保护通话 通过检查确认至少有一个元素可供选择：

if list_to_use:
    random.choice(list_to_use)

（请注意，如果有单个列表元素 那么它将永远被选中， 它没有随机性， 这可能是你想要的。）

Answer 3

如果每个参与者可以向同一个人赠送多个礼物，您可以使用

import random

number_of_people = int(input("How many participants? "))
names = numbers = gifts = list()

for i in range(number_of_people):
    name = input(f"What is the name of person {i+1}? ")
    number = int(input(f"How many is {name} giving? "))
    names.append(name)
    numbers.append(number)

for name, number in zip(names, numbers):
    choices = [n for n in names if n != name] # Define a list of all the participants this participant can give to
    giving = [random.choice(choices) for _ in range(number)] # Randomly pick a participant from the list *number* times
    print(f'{name} is giving {giving}')

如果每个参与者最多可以向同一个人赠送一份礼物，则可以使用

import random

number_of_people = int(input("How many participants? "))
names = numbers = gifts = list()

for i in range(number_of_people):
    name = input(f"What is the name of person {i+1}? ")
    number = int(input(f"How many is {name} giving? "))
    names.append(name)
    numbers.append(number)

for name, number in zip(names, numbers):
    choices = [n for n in names if n != name]
    if number > len(choices): # The participant won't be able to give more than the maximum to be received
        print('INVALID')
        continue
    random.shuffle(choices) # Randomly shuffle the list
    giving = choices[:number] # Take *number* names from the list
    print(f'{name} is giving {giving}')

输入：

How many participants? 4
What is the name of person 1? Jannet
How many is Jannet giving? 3
What is the name of person 2? Bobby
How many is Bobby giving? 1
What is the name of person 3? Symone
How many is Symone giving? 2
What is the name of person 4? Timmy
How many is Timmy giving? 3

输出：

Jannet is giving ['Symone', 'Bobby', 'Bobby']
Bobby is giving ['Timmy']
Symone is giving ['Timmy', 'Bobby']
Timmy is giving ['Bobby', 'Bobby', 'Jannet']