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>
(cherry picked from commit b4fc44bb2d209182390b4f9fdf074a46b0165a2f)

Co-authored-by: Chris Griffith <chris@cdgriffith.com>

diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index eecb1e7f253fbaf55e3e60a022d6664ab5720ef2..d4d04a5c3436a6879348f9291d67aadb535dda67 100644 (file)
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -1416,10 +1416,8 @@ class Popen(object):
                 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 (file)
index 0000000..290d7fb
--- /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.