TheAlgorithms/Python · error · ValueError

index out of range

Error message

index out of range

What it means

Raised by index_2d_array_in_1d() in data_structures/arrays/index_2d_array_in_1d.py when the flat index is negative or >= rows * cols. The function validates the linear index against the total element count before computing array[index // cols][index % cols], so this fires only when the array itself is non-empty.

Source

Thrown at data_structures/arrays/index_2d_array_in_1d.py:97

        ...
    ValueError: index out of range
    >>> index_2d_array_in_1d([[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11]], 12)
    Traceback (most recent call last):
        ...
    ValueError: index out of range
    >>> index_2d_array_in_1d([[]], 0)
    Traceback (most recent call last):
        ...
    ValueError: no items in array
    """
    rows = len(array)
    cols = len(array[0])

    if rows == 0 or cols == 0:
        raise ValueError("no items in array")

    if index < 0 or index >= rows * cols:
        raise ValueError("index out of range")

    return array[index // cols][index % cols]


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Clamp/validate before calling: 0 <= index < len(array) * len(array[0]).
2. Check loop bounds: use range(rows * cols), not +1; remember indexes are 0-based.
3. If the 2D list is ragged (rows of different lengths), normalize it first — the cols = len(array[0]) math assumes rectangular data.

Example fix

# before
for i in range(rows * cols + 1):
    val = index_2d_array_in_1d(grid, i)  # last i is out of range

# after
for i in range(rows * cols):
    val = index_2d_array_in_1d(grid, i)

rows, cols = len(array), len(array[0])
if not 0 <= index < rows * cols:
    raise IndexError(f'{index} outside 0..{rows*cols-1}')
val = index_2d_array_in_1d(array, index)

When it happens

Trigger: Calling index_2d_array_in_1d([[1,2],[3,4]], -1) or index_2d_array_in_1d([[1,2],[3,4]], 4) (max valid is 3). Also triggered by non-integer-like indexes after failed implicit coercion assumptions.

Common situations: Off-by-one loops (range(rows*cols + 1)), flat indexes computed from ragged/irregular 2D lists where len(array[0])*rows overestimates or underestimates actual counts, or passing a 1-based index to a 0-based API.

Related errors

• The parameter idx_original_string must be lower than len(bwt
• Invalid value of 'position'
• list index out of range
• The parameter idx_original_string must not be lower than 0.
• Both input arrays are empty.

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/e88bc64ce280cfbf. Report an issue: GitHub.