TheAlgorithms/Python · error · ValueError

Both input arrays are empty.

Error message

Both input arrays are empty.

What it means

Raised by find_median_sorted_arrays() in data_structures/arrays/median_two_array.py when both nums1 and nums2 are empty. A median of zero elements is undefined, so the function refuses rather than returning NaN or raising IndexError. Either array being non-empty is fine.

Source

Thrown at data_structures/arrays/median_two_array.py:42

        >>> find_median_sorted_arrays([0, 0], [0, 0])
        0.0

        >>> find_median_sorted_arrays([], [])
        Traceback (most recent call last):
            ...
        ValueError: Both input arrays are empty.

        >>> find_median_sorted_arrays([], [1])
        1.0

        >>> find_median_sorted_arrays([-1000], [1000])
        0.0

        >>> find_median_sorted_arrays([-1.1, -2.2], [-3.3, -4.4])
        -2.75
    """
    if not nums1 and not nums2:
        raise ValueError("Both input arrays are empty.")

    # Merge the arrays into a single sorted array.
    merged = sorted(nums1 + nums2)
    total = len(merged)

    if total % 2 == 1:  # If the total number of elements is odd
        return float(merged[total // 2])  # then return the middle element

    # If the total number of elements is even, calculate
    # the average of the two middle elements as the median.
    middle1 = merged[total // 2 - 1]
    middle2 = merged[total // 2]
    return (float(middle1) + float(middle2)) / 2.0


if __name__ == "__main__":
    import doctest

View on GitHub (pinned to f5988cc097)

Solutions

1. Check combined emptiness before calling: if not nums1 and not nums2: return None/0/handle.
2. Guard aggregation code so a median is only computed when at least one sample exists.
3. Treat this as a signal that your filter/window is too strict, not just an exception to suppress.

Example fix

# before
med = find_median_sorted_arrays(a, b)  # both empty

# after
med = find_median_sorted_arrays(a, b) if (a or b) else 0.0

if not nums1 and not nums2:
    return 0.0  # or None, per your convention
median = find_median_sorted_arrays(nums1, nums2)

try:
    median = find_median_sorted_arrays(nums1, nums2)
except ValueError:
    median = float('nan')  # explicitly mark no data

When it happens

Trigger: Calling find_median_sorted_arrays([], []), or both lists becoming empty after filtering (e.g. both filtered to values above a threshold that nothing meets).

Common situations: Aggregation over filtered datasets where filters can exclude everything, empty time windows in monitoring/metrics code, or initializing accumulators as empty lists and computing a median before adding data.

Related errors

• index out of range
• Invalid value of 'position'
• The parameter s must not be empty.
• The parameter bwt_string must not be empty.
• The parameter idx_original_string must not be lower than 0.

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/544de8e380a3940c. Report an issue: GitHub.