Why do I get "IndexError: list index out of range" when trying to add values to a nested list?

Question

I'm trying to put some data to my nested list.

n_list = []
n = int(input())

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

print(n_list)

Answer 1

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 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

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)