IndexError: list index out of range

Python · updated 2026-11-03

Raised when a list (or tuple) is subscripted with an index past its end, or a negative index past its start. The traceback points at the exact line; the list was shorter than the code expected.

Traceback (most recent call last):
  File "/app/report.py", line 22, in <module>
    main()
  File "/app/report.py", line 18, in main
    latest = rows[0]
             ~~~~^^^
IndexError: list index out of range

Quick fix

Check that the list has the item before you read it. For "first item or nothing", use next(iter(items), None) or test if items: first. If the list should never be empty, find out why it was: an empty query result or API response is the usual cause.

Print or log len(items) right before the failing line.
If empty is a valid state, handle it: if not items: return None.
For the first match, use next((x for x in items if ...), None) instead of a list and [0].
In loops, iterate over the items or use enumerate instead of range(len(...)) with manual offsets.

python

rows = fetch_rows(customer_id)

# Before: crashes when the query returns nothing
# latest = rows[0]

latest = rows[0] if rows else None
if latest is None:
    log.warning("no rows for customer %s", customer_id)
    return None

Why it happens

An empty result from a query or API

A filter that matches nothing, a new account with no data yet, or a paginated API returning an empty last page gives you [], and [0] on it raises this error.

Off-by-one in a loop

range(len(items) + 1), comparing items[i + 1] on the last iteration, or a stale length after removing items while looping all read one position too far.

Splitting a string that lacks the separator

line.split(',')[1] fails when the line has no comma. Header lines, blank lines and malformed rows in CSV or log files are the usual culprits.

Reading sys.argv without the argument

sys.argv[1] raises IndexError when the script runs without arguments, for example from a scheduler that omits them.

Other fixes

For text splitting, use str.partition or check len(parts) before indexing.
Use argparse instead of sys.argv indexing so missing arguments produce a clear usage message.
Do not catch IndexError broadly around large blocks: it hides the empty-data case you want to see.

Same error, other wording

IndexError: tuple index out of range
IndexError: string index out of range
IndexError: pop from empty list

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