From: Serhiy Storchaka <storchaka@gmail.com>
Date: Wed, 10 Dec 2014 20:59:55 +0000 (+0200)
Subject: Issue #23016: A warning no longer produces AttributeError when the program
X-Git-Tag: v3.4.3rc1~241
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=60599525c509a962e8fb5897240d42a56c092961;p=thirdparty%2FPython%2Fcpython.git

Issue #23016: A warning no longer produces AttributeError when the program
is run with pythonw.exe.
---

diff --git a/Lib/test/test_warnings.py b/Lib/test/test_warnings.py
index 0f2e089408cc..fb01b83e0c86 100644
--- a/Lib/test/test_warnings.py
+++ b/Lib/test/test_warnings.py
@@ -631,6 +631,15 @@ class _WarningsTests(BaseTest, unittest.TestCase):
         finally:
             globals_dict['__file__'] = oldfile
 
+    def test_stderr_none(self):
+        rc, stdout, stderr = assert_python_ok("-c",
+            "import sys; sys.stderr = None; "
+            "import warnings; warnings.simplefilter('always'); "
+            "warnings.warn('Warning!')")
+        self.assertEqual(stdout, b'')
+        self.assertNotIn(b'Warning!', stderr)
+        self.assertNotIn(b'Error', stderr)
+
 
 class WarningsDisplayTests(BaseTest):
 
diff --git a/Lib/warnings.py b/Lib/warnings.py
index 5d5c9a9dcbc5..3a8fc5db6516 100644
--- a/Lib/warnings.py
+++ b/Lib/warnings.py
@@ -11,6 +11,9 @@ def showwarning(message, category, filename, lineno, file=None, line=None):
     """Hook to write a warning to a file; replace if you like."""
     if file is None:
         file = sys.stderr
+        if file is None:
+            # sys.stderr is None when ran with pythonw.exe - warnings get lost
+            return
     try:
         file.write(formatwarning(message, category, filename, lineno, line))
     except OSError:
diff --git a/Misc/NEWS b/Misc/NEWS
index 4807dc4065e1..d4cd62eb23c2 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -39,6 +39,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #23016: A warning no longer produces an AttributeError when the program
+  is run with pythonw.exe.
+
 - Issue #21775: shutil.copytree(): fix crash when copying to VFAT. An exception
   handler assumed that that OSError objects always have a 'winerror' attribute.
   That is not the case, so the exception handler itself raised AttributeError