Day of Year Calculator

from datetime import date, timedelta

def day_of_year(year: int, month: int, day: int) -> int:
    """Return the ordinal day of year (1-365/366)."""
    return date(year, month, day).timetuple().tm_yday

def is_leap_year(year: int) -> bool:
    return year % 4 == 0 and (year % 100 != 0 or year % 400 == 0)

def days_in_year(year: int) -> int:
    return 366 if is_leap_year(year) else 365

def iso_week_number(year: int, month: int, day: int) -> int:
    return date(year, month, day).isocalendar()[1]

def day_number_to_date(year: int, day_num: int):
    """Convert ordinal day number back to a date."""
    return date(year, 1, 1) + timedelta(days=day_num - 1)

def year_progress(year: int, month: int, day: int) -> float:
    day_num = day_of_year(year, month, day)
    total = days_in_year(year)
    return round(day_num / total * 100, 1)

# Examples
today = date.today()
y, m, d = today.year, today.month, today.day
print(f"Day of year: {day_of_year(y, m, d)}")
print(f"Week number: {iso_week_number(y, m, d)}")
print(f"Leap year: {is_leap_year(y)}")
print(f"Year progress: {year_progress(y, m, d)}%")
print(f"Day 100 of {y}: {day_number_to_date(y, 100)}")