python nested list access gives error in loop

Question

I am currently stuck on this error and I did not find a solution (that I understood) on Google:

TypeError: list indices must be integers or slices, not tuple

I try to do:

    for x in values:
        val1 = values[x][0]
        val2 = values[x][1]
        val3 = values[x][2]

        writer.writerow([val1,val2,val3])

values is a nested list. Every nested list has the same length.

I understand the error, but I don't get why I am getting it because if i do: print(values[400][0]), everything works out fine, no error, just the content of the list.

if you are satisfied with one of the answers, request you to accept one of them as answers. — gsb22
– gsb22, Commented Jan 22, 2021 at 19:22

Krishna Chaurasia · Accepted Answer · 2021-01-22 14:12:38Z

1

When you use for x in values where values is a list, x represent the elements so when you use values[x], you are trying to access the values list by a list index which gives you the error TypeError: list indices must be integers or slices, not tuple.

Try this code:

for x in values:
    val1 = x[0]
    val2 = x[1]
    val3 = x[2]

    writer.writerow([val1,val2,val3])

Or change your code to below to use index based access:

for i in range(len(values)):
    val1 = values[i][0]
    val2 = values[i][1]
    val3 = values[i][2]

    writer.writerow([val1,val2,val3])

edited Jan 22, 2021 at 14:12

answered Jan 22, 2021 at 14:07

Krishna Chaurasia

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1 Comment

gsb22 Over a year ago

suggesting to use range(len(values)) is not pythonic.

Mitchell Olislagers · Accepted Answer · 2021-01-22 14:07:48Z

1

By using for x in values, x will be the sublist of you values list. If you try to index your main list by calling values[x], this will throw an error, as you can not index a list using a list. What you want is this

for x in values:
        val1 = x[0]
        val2 = x[1]
        val3 = x[2]

answered Jan 22, 2021 at 14:07

Mitchell Olislagers

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1 Comment

Murf Over a year ago

that makes perfect sense, thanks for explaining

Timur Shtatland · Accepted Answer · 2021-01-22 14:08:53Z

1

The issue is with the for loop: you need to write it like so to prevent the error:

for x in range(len(values)):
    val1 = values[x][0]
    val2 = values[x][1]
    val3 = values[x][2]

    writer.writerow([val1,val2,val3])

Better still, use this:

for x in values:
    writer.writerow([x[i] for i in range(3)])

answered Jan 22, 2021 at 14:08

Timur Shtatland

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Comments

gsb22 · Accepted Answer · 2021-01-22 14:09:58Z

1

As you mentioned, values is a list of lists.

Example. = [[1,2,3], [3,4,5], [9,10,11]]

So when you do for x in values:, you are taking out each list one by one, so now the x is a simple list. x = [1,2,3] in first iteration.

So, when you do values[x][0], you are doing values[[1,2,3]][0], which doesn't make sense, because list should be indexed with numbers.

Correct code would be

for x in values:
        val1 = x[0]
        val2 = x[1]
        val3 = x[2]
    writer.writerow([val1,val2,val3])

answered Jan 22, 2021 at 14:09

gsb22

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