IndexError: list index out of range

What you see

names = ["ada", "grace", "linus"]
print(names[3])

Traceback (most recent call last):
  File "/home/me/project/main.py", line 2, in <module>
    print(names[3])
          ~~~~~^^^
IndexError: list index out of range

What it means

A list of three items has positions 0, 1 and 2. Position 3 does not exist. Negative indexes count from the end, so -1 to -3 are valid here and -4 is not.

Strings and tuples give the same error with their own name: "string index out of range", "tuple index out of range".

Why it happens

• Counting from 1. names[len(names)] is one past the end; the last item is names[len(names) - 1], or simply names[-1].
• A loop that goes one too far, such as for i in range(len(names) + 1).
• An empty list. results[0] fails when the search found nothing.
• A command-line argument that was not given. sys.argv[1] fails when the script runs with no arguments.
• Removing items from a list while looping over its indexes, so the list gets shorter than the range.

How to fix it

Loop over the items, not over numbers, and there is no index to get wrong:

for name in names:
    print(name)

for i, name in enumerate(names):   # when you need the position too
    print(i, name)

Check before taking the first or last item of a list that may be empty:

if results:
    first = results[0]

For arguments, use argparse, which prints a usage message instead of an IndexError.

How each Python version words it

Run on CPython 3.9.6, 3.10.22, 3.11.17, 3.12.15, 3.13.17, 3.14.9 and 3.15.1, on October 25, 2026.

The wording is the same in every version here.