earthy.py

#!/usr/bin/env python3.7 

import urllib.request
import shutil
import json
import os
from datetime import date, timedelta

OUTPUT_PATH = "/tmp/"
IMAGE_LIST_URL_BASE = "http://epic.gsfc.nasa.gov/api/images.php?date="
IMAGE_URL_BASE = "http://epic.gsfc.nasa.gov/epic-archive/"
IMAGE_FORMAT = "png"

def image_list(idate):
    return json.loads(urllib.request.urlopen(IMAGE_LIST_URL_BASE + idate.strftime("%Y-%m-%d")).read().decode('utf-8'))

def get_file(url, out_file):
    print("Getting {}".format(url))
    with urllib.request.urlopen(url) as response, open(out_file, 'wb') as out_file:
        shutil.copyfileobj(response, out_file)
    print("Wrote {}".format(out_file))


if __name__ == '__main__':
    today = date.today()

    while True:
        print("Checking images for {}".format(today))

        if not image_list(today):
            today = today - timedelta(1)
            continue

        img_name = image_list(today)[-1][u'image'] + "." + IMAGE_FORMAT
        out_file = OUTPUT_PATH + img_name

        if not os.path.isfile(out_file):
            url = IMAGE_URL_BASE + IMAGE_FORMAT + "/" + img_name
            get_file(url, out_file)
        else:
            print("{} exists".format(out_file))

        break