add check if downloaded file has changed on server before downloading

tools/generator.py

@@ -7,15 +7,22 @@ from inspect import currentframe, getframeinfo
 from os import path
 
 import requests
+from dateutil.parser import parse as parsedate
 
 
 def download_to_file(url, file):
     user_agent = {
         "User-agent": "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:46.0) Gecko/20100101 Firefox/46.0"}
-    r = requests.get(url, headers=user_agent)
-    with open(file, 'wb') as fd:
-        for chunk in r.iter_content(4096):
-            fd.write(chunk)
+    r = requests.head(url, headers=user_agent)
+    url_datetime = parsedate(r.headers['Last-Modified']).astimezone()
+    file_datetime = datetime.datetime.fromtimestamp(
+        path.getmtime(file)).astimezone()
+
+    if(url_datetime > file_datetime):
+        r = requests.get(url, headers=user_agent)
+        with open(file, 'wb') as fd:
+            for chunk in r.iter_content(4096):
+                fd.write(chunk)
 
 
 def download(url):
@@ -40,7 +47,9 @@ def unique_sorted_warninglist(warninglist):
     warninglist['list'] = sorted(set(warninglist['list']))
     return warninglist
 
+
 def write_to_file(warninglist, dst):
     with open(get_abspath_list_file(dst), 'w') as data_file:
-        json.dump(unique_sorted_warninglist(warninglist), data_file, indent=2, sort_keys=True)
+        json.dump(unique_sorted_warninglist(warninglist),
+                  data_file, indent=2, sort_keys=True)
         data_file.write("\n")