From 0c2dd0c0a9498422645a2805a955b9a898298bc6 Mon Sep 17 00:00:00 2001
From: Victor Stinner <victor.stinner@gmail.com>
Date: Fri, 23 Aug 2013 19:19:15 +0200
Subject: [PATCH] Close #17702: On error, os.environb now removes suppress the
 except context when raising a new KeyError with the original key.

---
 Lib/os.py           | 4 ++--
 Lib/test/test_os.py | 3 +++
 Misc/NEWS           | 3 +++
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/Lib/os.py b/Lib/os.py
index 06616c64d87..87689cc2690 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -673,7 +673,7 @@ class _Environ(MutableMapping):
             value = self._data[self.encodekey(key)]
         except KeyError:
             # raise KeyError with the original key value
-            raise KeyError(key)
+            raise KeyError(key) from None
         return self.decodevalue(value)
 
     def __setitem__(self, key, value):
@@ -689,7 +689,7 @@ class _Environ(MutableMapping):
             del self._data[encodedkey]
         except KeyError:
             # raise KeyError with the original key value
-            raise KeyError(key)
+            raise KeyError(key) from None
 
     def __iter__(self):
         for key in self._data:
diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index 2db030e508a..fbf6c0cf7e5 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -644,10 +644,13 @@ class EnvironTests(mapping_tests.BasicTestMappingProtocol):
         with self.assertRaises(KeyError) as cm:
             os.environ[missing]
         self.assertIs(cm.exception.args[0], missing)
+        self.assertTrue(cm.exception.__suppress_context__)
 
         with self.assertRaises(KeyError) as cm:
             del os.environ[missing]
         self.assertIs(cm.exception.args[0], missing)
+        self.assertTrue(cm.exception.__suppress_context__)
+
 
 class WalkTests(unittest.TestCase):
     """Tests for os.walk()."""
diff --git a/Misc/NEWS b/Misc/NEWS
index bfb2fd8d8f0..81ad8f5d8fc 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -66,6 +66,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #17702: On error, os.environb now removes suppress the except context
+  when raising a new KeyError with the original key.
+
 - Issue #18755: Fixed the loader used in imp to allow get_data() to be called
   multiple times.