TheAlgorithms/Python · error · ValueError

Invalid range specified.

Error message

Invalid range specified.

What it means

Raised by PrefixSum.get_sum() in data_structures/arrays/prefix_sum.py when the requested [start, end] range is invalid for the populated array: start < 0, end >= len(prefix_sum), or start > end. Valid ranges are inclusive on both ends within array bounds.

Source

Thrown at data_structures/arrays/prefix_sum.py:54

        ValueError: The array is empty.
        >>> PrefixSum([1,2,3]).get_sum(-1, 2)
        Traceback (most recent call last):
        ...
        ValueError: Invalid range specified.
        >>> PrefixSum([1,2,3]).get_sum(2, 3)
        Traceback (most recent call last):
        ...
        ValueError: Invalid range specified.
        >>> PrefixSum([1,2,3]).get_sum(2, 1)
        Traceback (most recent call last):
        ...
        ValueError: Invalid range specified.
        """
        if not self.prefix_sum:
            raise ValueError("The array is empty.")

        if start < 0 or end >= len(self.prefix_sum) or start > end:
            raise ValueError("Invalid range specified.")

        if start == 0:
            return self.prefix_sum[end]

        return self.prefix_sum[end] - self.prefix_sum[start - 1]

    def contains_sum(self, target_sum: int) -> bool:
        """
        The function returns True if array contains the target_sum,
        False otherwise.

        Runtime : O(n)
        Space: O(n)

        >>> PrefixSum([1,2,3]).contains_sum(6)
        True
        >>> PrefixSum([1,2,3]).contains_sum(5)
        True

View on GitHub (pinned to f5988cc097)

Solutions

1. Remember both bounds are inclusive: the last valid end is len(arr) - 1, not len(arr).
2. Normalize arguments before calling: if start > end: start, end = end, start.
3. Validate: 0 <= start <= end < len(arr) before invoking get_sum.

Example fix

# before
ps.get_sum(0, len(arr))  # end one past the last index

# after
ps.get_sum(0, len(arr) - 1)  # inclusive end

n = len(arr)
start, end = max(0, start), min(end, n - 1)
if start > end:
    raise ValueError('empty normalized range')
total = ps.get_sum(start, end)

When it happens

Trigger: Calling get_sum(2, 3) or get_sum(2, 1) on PrefixSum([1,2,3]) (end 3 out of bounds; start > end), get_sum(-1, 2), or get_sum(0, n) where n == len(arr) — the classic inclusive-end off-by-one.

Common situations: Treating end as exclusive when it is inclusive (passing len(arr) instead of len(arr)-1), reversed bounds from swapped arguments, or ranges computed from user input without bound checks.

Related errors

• The array is empty.
• The parameter idx_original_string must be lower than len(bwt
• index out of range
• Invalid value of 'position'
• list index out of range

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/84d37d89ad8f30d5. Report an issue: GitHub.