(CSV) IndexError: list index out of range in Python

(CSV) IndexError: list index out of range in Python #

The Python CSV "IndexError: list index out of range" occurs when we try to access a list at an index out of range, e.g. an empty row in a CSV file. To solve the error, check if the row isn't empty before accessing it at index, or check if the index exists in the list.

Here is an example of how the error occurs.

Assume we have the following csv file.

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first_name,last_name

Alice,Smith
Bob,Smith
Carl,Smith

And we are trying to read it like:

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import csv

with open('employees.csv', newline='', encoding='utf-8') as csvfile:
    csv_reader = csv.reader(csvfile, delimiter=',')

    for row in csv_reader:
        # ⛔️ IndexError: list index out of range
        print(row[0])

One way to solve the error is to check if the list contains any elements before accessing it at an index.

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import csv

with open('employees.csv', newline='', encoding='utf-8') as csvfile:
    csv_reader = csv.reader(csvfile, delimiter=',')

    for row in csv_reader:
        if row:  # 👈️ check if row contains items
            print(row[0])

The if statement checks if the list is truthy on each iteration.

All values that are not truthy are considered falsy. The falsy values in Python are:

• constants defined to be falsy: None and False.
• 0 (zero) of any numeric type
• empty sequences and collections: "" (empty string), () (empty tuple), [] (empty list), {} (empty dictionary), set() (empty set), range(0) (empty range).

Alternatively, you can check whether the specific index you are trying to access exists in the list.

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import csv

with open('employees.csv', newline='', encoding='utf-8') as csvfile:
    csv_reader = csv.reader(csvfile, delimiter=',')

    idx = 1

    for row in csv_reader:
        if len(row) > idx:
            print(row[idx])

The len() function returns the length (the number of items) of an object.

The argument the function takes may be a sequence (a string, tuple, list, range or bytes) or a collection (a dictionary, set, or frozen set).

This means that you can check if the list's length is greater than the index you are trying to access.

Alternatively, you can use a try/except block to handle the error.

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import csv

with open('employees.csv', newline='', encoding='utf-8') as csvfile:
    csv_reader = csv.reader(csvfile, delimiter=',')

    for row in csv_reader:
        try:
            print(row[1])
        except IndexError:
            print('except block ran')
            continue

We try to access the list of the current iteration at index 1, and if an IndexError is raised, we can handle it in the except block or continue to the next iteration.

Conclusion #

The Python CSV "IndexError: list index out of range" occurs when we try to access a list at an index out of range, e.g. an empty row in a CSV file. To solve the error, check if the row isn't empty before accessing it at index, or check if the index exists in the list.