commit f8a3485dcd41a00c5e99c5be6adc67cb2638b366
author Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> Mon Feb 26 08:22:24 2018 -0800
committer GitHub <noreply@github.com> Mon Feb 26 08:22:24 2018 -0800
tree 78d6cfd847e877c55568adf3fec9583acb5269eb
parent a9e0b070b3e36701d0139361c769d374c4aacf1a

Revert unneccessary changes made in bpo-30296 and apply other improvements. (GH-2624)

(cherry picked from commit 3f2e6f15d64d81633b1fc0b308afc0d6e9026b61)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Lib/urllib/request.py

diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index 2b76942..5b962f7 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -1286,7 +1286,8 @@
         h.set_debuglevel(self._debuglevel)
 
         headers = dict(req.unredirected_hdrs)
-        headers.update((k, v) for k, v in req.headers.items() if k not in headers)
+        headers.update({k: v for k, v in req.headers.items()
+                        if k not in headers})
 
         # TODO(jhylton): Should this be redesigned to handle
         # persistent connections?