From 4d2957c1b9a915f76da418e89bf9b5add141ca3e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?R=C3=A9mi=20Lapeyre?= <remi.lapeyre@lenstra.fr>
Date: Mon, 20 Sep 2021 17:09:05 +0200
Subject: [PATCH] bpo-40497: Fix handling of check in subprocess.check_output()
 (GH-19897)
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Co-authored-by: Tal Einat <taleinat@gmail.com>
Co-authored-by: Łukasz Langa <lukasz@langa.pl>
---
 Lib/subprocess.py                                         | 5 +++--
 Lib/test/test_subprocess.py                               | 8 ++++++++
 .../next/Library/2020-10-18-09-42-53.bpo-40497.CRz2sG.rst | 4 ++++
 3 files changed, 15 insertions(+), 2 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2020-10-18-09-42-53.bpo-40497.CRz2sG.rst

diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index dd1174ee59a..33f022f8fce 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -405,8 +405,9 @@ def check_output(*popenargs, timeout=None, **kwargs):
     decoded according to locale encoding, or by "encoding" if set. Text mode
     is triggered by setting any of text, encoding, errors or universal_newlines.
     """
-    if 'stdout' in kwargs:
-        raise ValueError('stdout argument not allowed, it will be overridden.')
+    for kw in ('stdout', 'check'):
+        if kw in kwargs:
+            raise ValueError(f'{kw} argument not allowed, it will be overridden.')
 
     if 'input' in kwargs and kwargs['input'] is None:
         # Explicitly passing input=None was previously equivalent to passing an
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 87967ca7f3c..3af523e8346 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -171,6 +171,14 @@ class ProcessTestCase(BaseTestCase):
                 [sys.executable, "-c", "print('BDFL')"])
         self.assertIn(b'BDFL', output)
 
+        with self.assertRaisesRegex(ValueError,
+                "stdout argument not allowed, it will be overridden"):
+            subprocess.check_output([], stdout=None)
+
+        with self.assertRaisesRegex(ValueError,
+                "check argument not allowed, it will be overridden"):
+            subprocess.check_output([], check=False)
+
     def test_check_output_nonzero(self):
         # check_call() function with non-zero return code
         with self.assertRaises(subprocess.CalledProcessError) as c:
diff --git a/Misc/NEWS.d/next/Library/2020-10-18-09-42-53.bpo-40497.CRz2sG.rst b/Misc/NEWS.d/next/Library/2020-10-18-09-42-53.bpo-40497.CRz2sG.rst
new file mode 100644
index 00000000000..067c48626c3
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-10-18-09-42-53.bpo-40497.CRz2sG.rst
@@ -0,0 +1,4 @@
+:meth:`subprocess.check_output` now raises :exc:`ValueError` when the
+invalid keyword argument *check* is passed by user code. Previously
+such use would fail later with a :exc:`TypeError`.
+Patch by Rémi Lapeyre.