Backport 1.151 and 1.152:

Treat file://localhost/ as local too (same as file:/ and file:///).
Fixes #607789, bugfix candidate.

Lib/urllib.py

@@ -399,7 +399,7 @@ class URLopener:
 
     def open_file(self, url):
         """Use local file or FTP depending on form of URL."""
-        if url[:2] == '//' and url[2:3] != '/':
+        if url[:2] == '//' and url[2:3] != '/' and url[2:12].lower() != 'localhost/':
             return self.open_ftp(url)
         else:
             return self.open_local_file(url)