TheAlgorithms/Python · error · ValueError

List is empty

Error message

List is empty

What it means

average_absolute_deviation() computes the mean absolute deviation of a list of numbers; it raises ValueError('List is empty') when nums is falsy because the mean (and hence the deviation) is undefined for zero elements.

Source

Thrown at maths/average_absolute_deviation.py:20

    """
    Return the average absolute deviation of a list of numbers.
    Wiki: https://en.wikipedia.org/wiki/Average_absolute_deviation

    >>> average_absolute_deviation([0])
    0.0
    >>> average_absolute_deviation([4, 1, 3, 2])
    1.0
    >>> average_absolute_deviation([2, 70, 6, 50, 20, 8, 4, 0])
    20.0
    >>> average_absolute_deviation([-20, 0, 30, 15])
    16.25
    >>> average_absolute_deviation([])
    Traceback (most recent call last):
        ...
    ValueError: List is empty
    """
    if not nums:  # Makes sure that the list is not empty
        raise ValueError("List is empty")

    average = sum(nums) / len(nums)  # Calculate the average
    return sum(abs(x - average) for x in nums) / len(nums)


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Check the list is non-empty before calling; skip or default when it is empty.
2. Log which input produced the empty list to find the data pipeline issue.
3. If aggregating many groups, wrap per-group so one empty group doesn't abort the run.

Example fix

# before
mad = average_absolute_deviation(data)

# after
mad = average_absolute_deviation(data) if data else 0.0

if not nums:
    raise ValueError("cannot compute average absolute deviation of empty data")

def has_elements(nums: list[float]) -> bool:
    return isinstance(nums, list) and len(nums) > 0

try:
    mad = average_absolute_deviation(nums)
except ValueError as e:
    if str(e) == "List is empty":
        mad = 0.0  # or skip record
    else:
        raise

When it happens

Trigger: average_absolute_deviation([]), or passing a list populated by a filter/slice that ended up empty, e.g. average_absolute_deviation([x for x in data if x > 100]).

Common situations: Empty datasets after filtering; API responses returning empty arrays; batch jobs where one input group has no rows.

Related errors

• List is empty
• successes must be lower or equal to trials
• the function is defined for non-negative integers
• prob has to be in range of 1 - 0
• Not a Number

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/f60da53847c60f0a. Report an issue: GitHub.