gh-98966: Handle stdout=subprocess.STDOUT

ptsneves · ptsneves · commit b7d2917081d5 · 2022-11-01T16:17:02.000+01:00
Explicitly handle the case where stdout=STDOUT
as otherwise the existing error handling gets
confused and reports hard to understand errors.
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
@@ -854,6 +854,8 @@ def __init__(self, args, bufsize=-1, executable=None,
             if creationflags != 0:
                 raise ValueError("creationflags is only supported on Windows "
                                  "platforms")
+            if stdout is STDOUT:
+                raise ValueError("STDOUT can only be used for stderr")
 
         self.args = args
         self.stdin = None
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
@@ -1695,6 +1695,13 @@ def test_capture_output(self):
         self.assertIn(b'BDFL', cp.stdout)
         self.assertIn(b'FLUFL', cp.stderr)
 
+    def test_stdout_stdout(self):
+        # run() refuses to accetp stdout=STDOUT
+        with self.assertRaises(ValueError,
+                msg=("STDOUT can only be used for stderr")) as c:
+                output = self.run_python("print('will not be run')",
+                                         stdout=subprocess.STDOUT)
+
     def test_stdout_with_capture_output_arg(self):
         # run() refuses to accept 'stdout' with 'capture_output'
         tf = tempfile.TemporaryFile()
