TheAlgorithms/Python · error · ValueError

Useful years cannot be less than 1

Error message

Useful years cannot be less than 1

What it means

Raised by straight_line_depreciation() when useful_years is an int but < 1. range(useful_years) would produce no periods, so a zero or negative asset life is rejected. This check runs after the isinstance check, so the value is guaranteed integral when it fires.

Source

Thrown at financial/straight_line_depreciation.py:59

    :param residual_value: Residual value of the asset at the end of its useful life
    :return: A list of annual depreciation expenses over the asset's useful life
    >>> straight_line_depreciation(10, 1100.0, 100.0)
    [100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0, 100.0]
    >>> straight_line_depreciation(6, 1250.0, 50.0)
    [200.0, 200.0, 200.0, 200.0, 200.0, 200.0]
    >>> straight_line_depreciation(4, 1001.0)
    [250.25, 250.25, 250.25, 250.25]
    >>> straight_line_depreciation(11, 380.0, 50.0)
    [30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0, 30.0]
    >>> straight_line_depreciation(1, 4985, 100)
    [4885.0]
    """

    if not isinstance(useful_years, int):
        raise TypeError("Useful years must be an integer")

    if useful_years < 1:
        raise ValueError("Useful years cannot be less than 1")

    if not isinstance(purchase_value, (float, int)):
        raise TypeError("Purchase value must be numeric")

    if not isinstance(residual_value, (float, int)):
        raise TypeError("Residual value must be numeric")

    if purchase_value < 0.0:
        raise ValueError("Purchase value cannot be less than zero")

    if purchase_value < residual_value:
        raise ValueError("Purchase value cannot be less than residual value")

    # Calculate annual depreciation expense
    depreciable_cost = purchase_value - residual_value
    annual_depreciation_expense = depreciable_cost / useful_years

    # List of annual depreciation expenses

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass useful_years >= 1; the minimum meaningful schedule is one full-year period.
2. Guard computed lifespans and treat 0 as missing data rather than clamping silently.
3. Reject zero-life assets upstream — they usually indicate missing acquisition data.

Example fix

# before
life = retire_year - acquire_year  # 0 for same-year assets
straight_line_depreciation(life, 1250.0, 50.0)

# after
life = retire_year - acquire_year
if life < 1:
    raise ValueError(f'asset life must be >= 1 year, got {life}')
straight_line_depreciation(life, 1250.0, 50.0)

if not isinstance(useful_years, int) or useful_years < 1:
    raise ValueError('useful_years must be an int >= 1')
straight_line_depreciation(useful_years, purchase, residual)

try:
    sched = straight_line_depreciation(y, p, r)
except ValueError as exc:
    if 'less than 1' in str(exc):
        raise ValueError(f'invalid asset life: {y}') from exc
    raise

When it happens

Trigger: Calling straight_line_depreciation(0, 1250.0, 50.0) or with a negative int such as -3.

Common situations: Lifespans computed as (retire_year - acquire_year) that hit 0 for same-year assets, config placeholders of 0 meaning 'not set', or sign errors from data entry.

Related errors

• number_of_years must be > 0
• nominal_annual_percentage_rate must be >= 0
• Discount rate cannot be negative
• Cash flows list cannot be empty
• Window size must be a positive integer

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/b56e9dddb0dd1ed3. Report an issue: GitHub.