労働週計算機

from datetime import date, timedelta

def get_iso_week(d: date) -> tuple[int, int]:
    """Return (iso_year, iso_week) for a date"""
    iso = d.isocalendar()
    return iso.year, iso.week

def get_monday_of_week(d: date) -> date:
    """Get the Monday of the week containing date d"""
    days_since_monday = d.weekday()  # Monday=0, Sunday=6
    return d - timedelta(days=days_since_monday)

def count_work_weeks(start: date, end: date) -> list[dict]:
    """List all ISO work weeks in a date range"""
    weeks = []
    current = get_monday_of_week(start)

    while current <= end:
        iso_year, iso_week = get_iso_week(current)
        friday = current + timedelta(days=4)
        weeks.append({
            'iso_year': iso_year,
            'iso_week': iso_week,
            'week_label': f'W{iso_week:02d}',
            'start': current,
            'end': friday,
            'month': current.strftime('%B %Y'),
        })
        current += timedelta(weeks=1)

    return weeks

# Usage
start = date(2026, 1, 1)
end = date(2026, 3, 31)
weeks = count_work_weeks(start, end)

print(f"Total work weeks: {len(weeks)}")
for w in weeks[:5]:  # Show first 5
    print(f"  {w['week_label']} ({w['iso_year']}): {w['start']} - {w['end']}")