TheAlgorithms/Python · error · ValueError

number_of_years must be > 0

Error message

number_of_years must be > 0

What it means

Raised by apr_interest() in financial/interest.py when number_of_years <= 0. The function computes annual-percentage-rate interest by delegating to compound_interest with number_of_years * 365 periods, so a non-positive year count is meaningless and rejected before any math runs. It is a deliberate input-contract check, not a numerical failure.

Source

Thrown at financial/interest.py:106

    >>> apr_interest(10000.0, 0.05, 1)
    512.6749646744732
    >>> apr_interest(0.5, 0.05, 3)
    0.08091115361317736
    >>> apr_interest(10000.0, 0.06, -4)
    Traceback (most recent call last):
        ...
    ValueError: number_of_years must be > 0
    >>> apr_interest(10000.0, -3.5, 3.0)
    Traceback (most recent call last):
        ...
    ValueError: nominal_annual_percentage_rate must be >= 0
    >>> apr_interest(-5500.0, 0.01, 5)
    Traceback (most recent call last):
        ...
    ValueError: principal must be > 0
    """
    if number_of_years <= 0:
        raise ValueError("number_of_years must be > 0")
    if nominal_annual_percentage_rate < 0:
        raise ValueError("nominal_annual_percentage_rate must be >= 0")
    if principal <= 0:
        raise ValueError("principal must be > 0")

    return compound_interest(
        principal, nominal_annual_percentage_rate / 365, number_of_years * 365
    )


if __name__ == "__main__":
    import doctest

    doctest.testmod()

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass a strictly positive number of years: at minimum 1 (or a positive fraction for partial years).
2. If the value is user-supplied or computed, validate it at the call site before invoking apr_interest.
3. If 0 years is legitimately possible in your flow, short-circuit it: return the principal unchanged instead of calling the function.

Example fix

# before
apr_interest(10000.0, 0.05, end_year - start_year)  # ValueError when equal

# after
years = end_year - start_year
value = 10000.0 if years <= 0 else apr_interest(10000.0, 0.05, years)

years = end_year - start_year
if years <= 0:
    raise ValueError(f"term must be positive, got {years}")
apr_interest(10000.0, 0.05, years)

try:
    value = apr_interest(p, r, y)
except ValueError as exc:
    if 'number_of_years' in str(exc):
        raise ValueError(f'invalid term: {y}') from exc
    raise

When it happens

Trigger: Calling apr_interest(principal, rate, years) with years = 0 or a negative value, e.g. apr_interest(10000.0, 0.01, 0) or apr_interest(10000.0, 0.01, -3). Note years is checked first, so a bad years value masks bad rate/principal.

Common situations: Passing a computed duration that can be 0 (e.g. (end_year - start_year) before validation), unit confusion (months passed where years expected, giving fractional-but-positive values that silently work), or defaults of 0 in a config dict.

Related errors

• 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
• Useful years cannot be less than 1

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/ec629becf66ac95e. Report an issue: GitHub.