From f915f11a0c30fbe28a6083110b64077aedecde27 Mon Sep 17 00:00:00 2001
From: Eli Schwartz <eschwartz@archlinux.org>
Date: Sun, 26 May 2019 21:29:41 -0400
Subject: [PATCH] py3: fix dict.keys() usage

micro-optimize: if r.keys() is empty, r is empty first.
---
 src/calibre/ebooks/chm/metadata.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/calibre/ebooks/chm/metadata.py b/src/calibre/ebooks/chm/metadata.py
index 8384263b4b..a822428fde 100644
--- a/src/calibre/ebooks/chm/metadata.py
+++ b/src/calibre/ebooks/chm/metadata.py
@@ -14,6 +14,7 @@ from calibre.ebooks.metadata import string_to_authors, MetaInformation
 from calibre.utils.logging import default_log
 from calibre.ptempfile import TemporaryFile
 from calibre import force_unicode
+from polyglot.builtins import iterkeys
 
 
 def _clean(s):
@@ -110,9 +111,8 @@ def _get_cover(soup, rdr):
             except:
                 # Probably invalid width, height aattributes, ignore
                 continue
-        l = r.keys()
-        l.sort()
-        if l:
+        if r:
+            l = sorted(iterkeys(r))
             ans = r[l[0]]
     # this link comes from the internal html, which is in a subdir
     if ans is not None: