inventory.stock-turnover

def stock_turnover(opening_stock: Money, closing_stock: Money, cost_of_sales: Money, period_days: int) -> StockTurnover

@dataclass(frozen=True)
class StockTurnover:
    """How fast stock moves, three ways."""

    #: (opening + closing) / 2, half-up to minor units
    average_stock: Money
    #: cost of sales / average stock, to 2 decimal places; null when average stock is zero
    turns: Optional[float]
    #: average stock / cost of sales x periodDays, to 1 decimal place; null when cost of sales is zero
    days_inventory_outstanding: Optional[float]
    #: closing stock / cost of sales x periodDays, to 1 decimal place; null when cost of sales is zero
    days_of_cover: Optional[float]

from fune.inventory.stock_turnover import stock_turnover  # inventory.stock-turnover@^1

from .inventory_stock_turnover_types import StockTurnover
from .math_round_div import round_div  ← from math.round-div ^1.0.0 · built alongside by fune
from .money_amount import Money, assert_same_currency, money  ← from money.amount ^1.0.0 · built alongside by fune


def _not_negative(name: str, amount: Money) -> None:
    if amount.minor < 0:
        raise ValueError("%s must not be negative, received %d" % (name, amount.minor))


def stock_turnover(opening_stock: Money, closing_stock: Money, cost_of_sales: Money, period_days: int) -> StockTurnover:
    """Turns, days inventory outstanding and days of cover. Each is one exact
    division rounded half-up, then made a float, so every language agrees.
    """
    assert_same_currency(opening_stock, closing_stock)
    assert_same_currency(opening_stock, cost_of_sales)
    _not_negative("openingStock", opening_stock)
    _not_negative("closingStock", closing_stock)
    _not_negative("costOfSales", cost_of_sales)
    if isinstance(period_days, bool) or not isinstance(period_days, int) or period_days < 1:
        raise ValueError("periodDays must be a whole number of days, at least 1, received %r" % (period_days,))
    both = opening_stock.minor + closing_stock.minor
    cogs = cost_of_sales.minor
    return StockTurnover(
        average_stock=money(round_div(both, 2, "half-up"), opening_stock.currency),
        turns=None if both == 0 else round_div(cogs * 200, both, "half-up") / 100,
        days_inventory_outstanding=None
        if cogs == 0
        else round_div(both * period_days * 10, cogs * 2, "half-up") / 10,
        days_of_cover=None if cogs == 0 else round_div(closing_stock.minor * period_days * 10, cogs, "half-up") / 10,
    )

Install

fune build

With that line in your source, in a Python project (language python in fune.project), fune build resolves it and its 2 dependencies, pins them in fune.lock, downloads only the Python package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. Or pin a range in fune.project and build in one step:

fune add inventory.stock-turnover

The manifest, vectors and README with only the Python implementation. Install it without the registry with fune add ./inventory.stock-turnover-1.0.0-python.fune, or fetch it from a terminal with fune pull inventory.stock-turnover@1.0.0:python.

The whole function, every language, is one file too: inventory.stock-turnover-1.0.0.fune, 14,658 bytes, sha256 9155bb345cfebcc9171de07f32cb2dbca138e4b611c2e5f980f793cbbc978314. It installs into a project of any language.

# fune: before inventory.stock-turnover

# fune: after inventory.stock-turnover

# fune: replace math.round-div in inventory.stock-turnover
# fune: replace money.amount in inventory.stock-turnover

# fune: step inventory.stock-turnover after <n|label>

More from the author

**Exact, then rounded once.** Each ratio is a single division of whole minor units, rounded half-up with `math.round-div` to hundredths (turns) or tenths (days), and only then turned into a float. So 0.005 turns is 0.01 in every language, where `Math.round(x * 100) / 100` and Python's `round(x, 2)` disagree. `averageStock` is rounded half-up to a minor unit for display; the ratios use the exact sum, not the rounded average.

**No answer is null, not zero or infinity.** Turns is null when average stock is zero; the two day counts are null when cost of sales is zero (stock that does not move has no cover horizon).

Use cost values throughout: turnover on sales value against stock at cost overstates it by the margin. Stock values and cost of sales may not be negative, the three amounts must share a currency, and periodDays must be at least 1.

Source: the standard definitions, e.g. CIMA Official Terminology (inventory turnover, inventory days).

Files