IndexError: list index out of range — how to fix

Traceback (most recent call last):
  File "main.py", line 3, in <module>
    print(items[3])
IndexError: list index out of range

Quick fix: Print len(items) and the index right before the failing line. Use range(len(items)) (not len + 1), iterate directly with for x in items, check if items: before items[0], and use sys.argv / split() results only after checking their length.

What it means

For items = ["a", "b", "c"], valid indexes are 0, 1, 2 and -1, -2, -3. items[3] or items[-4] raises IndexError. Related messages: string index out of range, tuple index out of range, pop from empty list.

Debug by printing just before the line:

print(len(items), i, items)

Note that slices never raise: items[5:10] returns [].

Cause 1: off-by-one in a loop

for i in range(len(items) + 1):   # goes one past the end
    print(items[i])

for i in range(1, len(items) + 1):  # 1-based thinking
    print(items[i])

Prefer iterating directly; use enumerate if you need the index:

for item in items:
    print(item)

for i, item in enumerate(items):
    print(i, item)

Comparing neighbours? Stop one early:

for i in range(len(items) - 1):
    if items[i] > items[i + 1]: ...

Or for a, b in zip(items, items[1:]):.

Cause 2: the list is empty

items[0] or items[-1] on [] fails. Common with filtered results, API responses and database queries.

if items:
    first = items[0]
else:
    first = None

# or
first = items[0] if items else None
first = next(iter(items), None)

Cause 3: sys.argv without arguments

import sys
filename = sys.argv[1]   # IndexError when run as: python script.py

sys.argv[0] is the script name. Check the length, or use argparse, which prints a usage message instead:

if len(sys.argv) < 2:
    sys.exit("usage: script.py FILE")

Cause 4: split() returned fewer parts

line = "alice"
name, age = line.split(",")[0], line.split(",")[1]   # IndexError

Lines in CSV or log files may be blank or malformed — especially a trailing empty line. Guard it:

parts = line.strip().split(",")
if len(parts) < 2:
    continue

Use the csv module for real CSV files, and str.partition(",") when you want exactly two parts without errors.

Cause 5: modifying a list while iterating by index

for i in range(len(items)):
    if items[i] < 0:
        items.pop(i)        # list shrinks; later i is out of range

Build a new list instead:

items = [x for x in items if x >= 0]

Cause 6: nested lists / 2D grids

grid[row][col] fails if rows have different lengths or you swapped row and column. Use len(grid) for rows and len(grid[row]) for that row's columns. When creating grids, use [[0] * cols for _ in range(rows)].

Cause 7: NumPy / pandas

IndexError: index 5 is out of bounds for axis 0 with size 5 is the NumPy equivalent. In pandas, df.iloc[n] raises IndexError: single positional indexer is out-of-bounds; check len(df) or df.empty first.

Last updated 2026-11-02.