From b4fc44bb2d209182390b4f9fdf074a46b0165a2f Mon Sep 17 00:00:00 2001
From: Chris Griffith <chris@cdgriffith.com>
Date: Thu, 11 Mar 2021 13:43:29 -0600
Subject: [PATCH] bpo-43423 Fix IndexError in subprocess _communicate function
 (GH-24777)

Check to make sure stdout and stderr are not empty before selecting an item from them in Windows subprocess._communicate.

Co-authored-by: Gregory P. Smith <greg@krypto.org>
---
 Lib/subprocess.py                                           | 6 ++----
 .../next/Library/2021-03-11-15-44-18.bpo-43423.rRomRD.rst   | 2 ++
 2 files changed, 4 insertions(+), 4 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2021-03-11-15-44-18.bpo-43423.rRomRD.rst

diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index e4ca5f500c21a7..d375514b2dd0a6 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -1535,10 +1535,8 @@ def _communicate(self, input, endtime, orig_timeout):
                 self.stderr.close()
 
             # All data exchanged.  Translate lists into strings.
-            if stdout is not None:
-                stdout = stdout[0]
-            if stderr is not None:
-                stderr = stderr[0]
+            stdout = stdout[0] if stdout else None
+            stderr = stderr[0] if stderr else None
 
             return (stdout, stderr)
 
diff --git a/Misc/NEWS.d/next/Library/2021-03-11-15-44-18.bpo-43423.rRomRD.rst b/Misc/NEWS.d/next/Library/2021-03-11-15-44-18.bpo-43423.rRomRD.rst
new file mode 100644
index 00000000000000..290d7fbd91800c
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-03-11-15-44-18.bpo-43423.rRomRD.rst
@@ -0,0 +1,2 @@
+:func:`subprocess.communicate` no longer raises an IndexError when there is an
+empty stdout or stderr IO buffer during a timeout on Windows.