Improve urlgrabber_compat load balancing

src/mio/urlgrabber_compat.py

+#!/usr/bin/python3
 #
 # Hackish compat library when urlgrabber is missing (MacOS)
 #
-try:
-    # Python 3
 from urllib.request import urlopen
-except ImportError:
-    # Python 2 fallback
-    from urllib2 import urlopen
+import urllib.parse
 import calendar
 import time
+import random
 
 INFO_FILETIME = object()
 
@@ -29,6 +27,7 @@ class CurlWrapper:
     
     def __getattr__(self, what):
         return getattr(self.url, what)
+
     pass
 
 class Compat: 
@@ -40,15 +39,23 @@ class Compat:
     class MirrorGroup:
         
         def __init__(self, grabber, urls):
-            self.urls = urls
+            self.urls = list(urls)
+            random.shuffle(self.urls)
+            self.mru = dict([ (u,0) for u in self.urls ])
             
         def urlopen(self, path):
             errors = []
-            for u in self.urls:
+            for u in reversed(sorted(self.urls, key=lambda u: self.mru[u])):
                 url = "%s/%s" % (u, path)
                 try:
-                    return CurlWrapper(urlopen(url))
+                    # print(u, self.mru[u], path)
+                    result = CurlWrapper(urlopen(url))
+                    self.mru[u] += 1
+                    return result
                 except IOError as e:
+                    # print(e.__class__, e)
+                    # TODO, penalize umreachable hosts?
+                    self.mru[u] /= 2
                     errors.append((url,e))
                     pass
             raise IOError("Failed to get '%s' (%s)" % (path, errors))