From 7669bfdedb8baeca2230430e219c97e700727777 Mon Sep 17 00:00:00 2001
From: Eli Schwartz <eschwartz@archlinux.org>
Date: Mon, 22 Jul 2019 20:25:53 -0400
Subject: [PATCH 12/71] simplify check for non-zero content in set()

There's no point in casting to list just to compare to [], since
set/list/tuple will evaluate to false when empty. So we can do less work
in fewer characters.
---
 src/calibre/gui2/email.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/calibre/gui2/email.py b/src/calibre/gui2/email.py
index 8b07edaa3e..1f348af3f5 100644
--- a/src/calibre/gui2/email.py
+++ b/src/calibre/gui2/email.py
@@ -429,7 +429,7 @@ class EmailMixin(object):  # {{{
                     dbfmts = self.library_view.model().db.formats(id, index_is_id=True)
                     formats = [f.lower() for f in (dbfmts.split(',') if dbfmts else
                         [])]
-                    if list(set(formats).intersection(available_input_formats())) != [] and list(set(fmts).intersection(available_output_formats())) != []:
+                    if set(formats).intersection(available_input_formats()) and set(fmts).intersection(available_output_formats()):
                         auto.append(id)
                     else:
                         bad.append(self.library_view.model().db.title(id, index_is_id=True))