generate cron jobs based on sunrise/sunset, independent of daylight savings time

solarcron.py

#!/usr/bin/env python3

import ephem
from datetime import datetime, timedelta, timezone

# don't generate any invocations until
SKIP_UNTIL = datetime(2021, 10, 16, 12, 0, 0)
# times to run per day
FOODS = 8
# thing to run
SCRIPT = "/home/pi/dispense.py"

sun=ephem.Sun()
# where you are
boulder=ephem.Observer()
boulder.lat='40:0:53.94'
boulder.lon='-105:16:13.96'
boulder.date=datetime.now().replace(hour=0, minute=0, second=0).astimezone(timezone.utc)

print("# {} {}".format(boulder.lat, boulder.lon))
if SKIP_UNTIL > datetime.now():
    print("# Skipping until {}".format(SKIP_UNTIL))
print()

def generate(sunrise, sunset):
    s = "# {} {} -> {} ({})".format(
        sunrise.date().isoformat(),
        sunrise.time().isoformat()[:8],
        sunset.time().isoformat()[:8],
	sunset - sunrise)
    print(s)

    # start one hour after sunrise
    start = sunrise + timedelta(hours=1)
    # stop 3/4 of the way between sunset and midnight
    midnight = datetime(sunset.year, sunset.month, sunset.day) + timedelta(days=1)
    nightoffset = 3.0 * ((midnight - sunset) / 4.0)
    stop = sunset + nightoffset
    step = (stop - start) / (FOODS - 1)

    cronline = "{:2d} {:2d} {:2d} {:2d} {} {} sleep {:2d} ; {}"
    for j in range(FOODS):
        t = start + j * step
        t -= timedelta(seconds=1)
        if t <= SKIP_UNTIL:
            print("# ", end='')
        print(cronline.format(t.minute, t.hour, t.day, t.month, "*", "root",
                              t.second, SCRIPT))

    print()

for i in range(7):
    sunrise = boulder.next_rising(sun)
    boulder.date = sunrise
    sunrise = ephem.localtime(sunrise)

    sunset  = boulder.next_setting(sun)
    boulder.date = sunset
    sunset  = ephem.localtime(sunset)

    generate(sunrise, sunset)