bpo-43423 Fix IndexError in subprocess _communicate function (GH-24777)

cdgriffith · gpshead · web-flow · commit b4fc44bb2d20 · 2021-03-11T11:43:29.000-08:00
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 &lt;greg@krypto.org&gt;
diff --git 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
@@ -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.

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+:func:`subprocess.communicate` no longer raises an IndexError when there is an
	`2`	`+empty stdout or stderr IO buffer during a timeout on Windows.`