Make fetch script usable with different years

fetch.py

@@ -1,16 +1,18 @@
+from datetime import datetime
 import os
 import requests
 import sys
 
-if len(sys.argv) != 2:
+if len(sys.argv) < 2:
     print("Usage: <fetch> day")
     sys.exit()
 day = sys.argv[1]
+year = sys.argv[2] if len(sys.argv) > 2 else str(datetime.now().year)
 
-URL = "https://adventofcode.com/2019/day/{}/input"
+URL = "https://adventofcode.com/{}/day/{}/input"
 SESSION_ID = os.environ["AOC_SESSION"]
 
-response = requests.get(URL.format(day), cookies={"session": SESSION_ID})
+response = requests.get(URL.format(year, day), cookies={"session": SESSION_ID})
 response.raise_for_status()
 
 with open("day{}.txt".format(day), "wt") as output_file: