CODEWITHSUNDEEP
pythonlistfor-loop
Jdubb
Jdubb

Reputation: 39

List index out of range error on simple python for loop

Can someone explain to me why this for loop doesn't work. I'm trying to use something like this in another program to loop through a list using this N as a parameter.

    N = [20,40,60,80]

    for j in N:
        print(j)
        for i in range(0,N[j]):
            print(i)

Thanks in advance!

Upvotes: 0

Views: 7056

Answers (3)

RoadRunner
RoadRunner

Reputation: 26335

Try:

for i in range(0,j):

Instead of:

for i in range(0,N[j]):

Since N[j] will access way beyond whats in the list, such as N[80], which doesn't exist. This is why you're getting a IndexError: list index out of range error.

To fix this, you need to apply range() on your outer loop:

for i in range(len(N)):
    print(i)
    for j in range(0, N[i]):
        print(j)

Which only looks at the indexes i of N when applying it to range() in the inner loop, instead of the actual elements, which are a lot larger.

If you want to access whats actually in the list with respect to an index, try this:

N = [20,40,60,80]
for i in range(len(N)):
    print(i, "->", N[i])

Which outputs:

0 -> 20
1 -> 40
2 -> 60
3 -> 80

If you want just the numbers:

for number in N:
    print(number)

If you want both the index and the number in a more pythonic manner:

for index, number in enumerate(N):
    print(index, "->", number)

Which outputs:

0 -> 20
1 -> 40
2 -> 60
3 -> 80

Upvotes: 0

Shailyn Ortiz
Shailyn Ortiz

Reputation: 766

you could use enumerate

N = [20,40,60,80]
for index, j in enumerate(N):
    print(j)
    for i in range(0,N[index]):
        print(i)

Upvotes: 0

GaryMBloom
GaryMBloom

Reputation: 5699

You're out of range, because j is taking the values of the elements of the N array, not the index. So, j is not 0, 1, 2, 3 but rather 20, 40, 60, 80. So, when you get to for i in range((0, N[j]), you're asking for N[20], which is well beyond the length of the N list.

You could do:

N = [20,40,60,80]

for j in range(len(N)):
#        ^^^^^^^^^^^^^
    print(j)
    for i in range(0,N[j]):
        print(i)

Upvotes: 3

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