Python错误：“IndexError：列表索引超出范围”

Question

I'm trying to put some data to my "nested list". I'm a beginner, please explain me, thank you all.

n_list = []
n = int(input())
for i in range (0,n):
    print(i)
    name = input()
    n_list[i].append(name)
    val = int(input())
    n_list[i].append(val)
print(n_list)

Answer 1

If you're appending to list, you don't need to use index (by using n_list[i] you're pointing to i-th element of the array):

n_list = []
n = int(input())
for i in range (0,n):
    print(i)
    name = input()
    n_list.append(name)
    val = int(input())
    n_list.append(val)
print(n_list)

I you want to nest lists, do this:

n_list = []
n = int(input())
for i in range (0,n):
    print(i)
    inner_list = []
    name = input()
    inner_list.append(name)
    val = int(input())
    inner_list.append(val)
    n_list.append(inner_list)
print(n_list)

Answer 2

The mistake is pretty simple and expected, so nothing to feel bad about.

The append function works in the following way (syntax):
    <list_name>.append(<item>)

is the name of the list and is the item to be inserted.

In your code,

n_list[i].append(name)

You are trying to append to the list present in i th index of n_list, which doesn't exist. So its showing the error

Answer 3

Like Andronicus said you dont need to use the index [i]. But you are talking about a 'nested list'. What you are trying to do is not 'nested'. Seems like you want to create a list of key/value objects:

n_list = []
n = int(input())
for i in range (0,n):
    print(i)
    name = input()
    val = int(input())
    n_list.append([name, val])
print(n_list)

Results in something like: [['myname', 2], ['yourname', 3]] or as a dictionary:

n_list = []
n = int(input())
for i in range (0,n):
    print(i)
    name = input()
    val = int(input())
    n_list.append({'name': name, 'value': val})
print(n_list)

Results in something like: [{'name': 'myname', 'value': 3}, {'name': 'yourname', 'value': 4}]

Answer 4

The problem is that you are trying to access the i -th item of an empty list. Since the list has 0 elements and you are asking for the i -th one, you get an error.

You could initialize a list with dummy values

n = int(input())
n_list = n * [None]

and then, write

n_list[i] = the_value

Answer 5

This one is working. the reasons why your method didn't work it's because you were identifying an index that doesn't yet exist

n_list[i]

the list has no elements. that's why you need to append() the new ones.

n_list = []
n = int(input("write list length: \n"))
for i in range (n):
    item = [] #create the nested list for each loop

    name = input("Write name : \n")
    item.append(name)

    val = int(input("write value : \n"))
    item.append(val)

    n_list.append(item)

print(n_list)