dates.add-business-days

def add_business_days(iso: str, days: int, holidays: Sequence[str]) -> str

from fune.dates.add_business_days import add_business_days  # dates.add-business-days@^1

from typing import Sequence

from .dates_add_days import epoch_day_from_iso, iso_from_epoch_day  ← from dates.add-days ^1.0.0 · built alongside by fune
from .dates_day_of_week import day_of_week  ← from dates.day-of-week ^1.0.0 · built alongside by fune


def add_business_days(iso: str, days: int, holidays: Sequence[str]) -> str:
    """The ``days``-th working day after ``iso`` (before it when negative),
    skipping Saturdays, Sundays and the listed holidays.

    The start date is never counted, so Friday + 1 and Saturday + 1 are both
    Monday, as in spreadsheet WORKDAY. Zero returns ``iso`` unchanged.
    """
    if isinstance(days, bool) or not isinstance(days, int):
        raise TypeError("days must be an integer, received %r" % (days,))
    day = epoch_day_from_iso(iso)
    # Every holiday is validated even when the move never reaches it, so a typo
    # in a calendar fails on the next run rather than in the year it matters.
    excluded = {epoch_day_from_iso(holiday) for holiday in holidays}

    step = -1 if days < 0 else 1
    weekday = day_of_week(iso)
    remaining = abs(days)
    while remaining > 0:
        day += step
        weekday = (weekday - 1 + step) % 7 + 1
        if weekday <= 5 and day not in excluded:
            remaining -= 1
    return iso_from_epoch_day(day)

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 dates.add-business-days

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

The whole function, every language, is one file too: dates.add-business-days-1.0.0.fune, 10,744 bytes, sha256 ca468a6c835a3956b1d871f90139f2c4867e6021e46ae57156363167f24361b1. It installs into a project of any language.

# fune: before dates.add-business-days

# fune: after dates.add-business-days

# fune: replace dates.add-days in dates.add-business-days
# fune: replace dates.day-of-week in dates.add-business-days

# fune: step dates.add-business-days after <n|label>

More from the author

It agrees with dates.business-days-between: from a working day `d`, businessDaysBetween(d, addBusinessDays(d, n, h), h) is n.

**Holidays are an argument, not a region.** Taking an explicit list keeps this capability universal: it works for any country, for an employer's own closure days, and for a court or exchange calendar, none of which a region code could express. For UK bank holidays, fetch them with dates.bank-holidays for each year the move can span and pass the dates in. That composition is a caller's choice rather than a dependency, so the capability never ships holiday data a caller did not ask for, and a year missing from that data fails in dates.bank-holidays, loudly, instead of here, quietly.

Holidays that fall at a weekend are not skipped twice, duplicates are harmless, and every holiday is validated even if the move never reaches it, so a typo in a calendar fails on the next run.

Pass enough holiday years. Moving 10 working days from 21 December needs the next January's holidays too; a list that stops at 31 December will count New Year's Day as a working day.

Files