TheAlgorithms/Python · error · ValueError

The array is empty.

Error message

The array is empty.

What it means

Raised by PrefixSum.get_sum() in data_structures/arrays/prefix_sum.py when the underlying prefix_sum list is empty — i.e. the PrefixSum was built (directly or effectively) from an empty array. The emptiness check runs before the range check, so any get_sum call on an empty structure raises this first.

Source

Thrown at data_structures/arrays/prefix_sum.py:51

        >>> PrefixSum([]).get_sum(0, 0)
        Traceback (most recent call last):
        ...
        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)

View on GitHub (pinned to f5988cc097)

Solutions

1. Check the source array is non-empty before constructing/querying: if data: ps = PrefixSum(data).
2. Ensure queries only run after data population completes (ordering, readiness flag).
3. Return a sentinel (0 or None) for empty data instead of calling get_sum.

Example fix

# before
ps = PrefixSum([])
total = ps.get_sum(0, 0)  # ValueError

# after
total = 0  # defined result for empty range
data = [x for x in source if keep(x)]
if data:
    total = PrefixSum(data).get_sum(0, len(data) - 1)

if not data:
    return 0  # no data, no range sums
ps = PrefixSum(data)
total = ps.get_sum(0, len(data) - 1)

When it happens

Trigger: Calling PrefixSum([]).get_sum(0, 0), or calling get_sum before any data was loaded into the structure. Empty arrays passed to the constructor produce an empty prefix_sum list.

Common situations: Querying a prefix-sum structure that was initialized but not yet populated, datasets that load asynchronously where a query races ahead of the data load, or empty query windows in data pipelines.

Related errors

• Invalid range specified.
• The parameter s must not be empty.
• The parameter bwt_string must not be empty.
• We need some text to work with.
• empty number list not allowed

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/12ce451f4da2abe8. Report an issue: GitHub.