From 0f38908684505905fd0890f4effbe6f683b39954 Mon Sep 17 00:00:00 2001
From: Ezio Melotti <ezio.melotti@gmail.com>
Date: Thu, 4 Apr 2013 02:09:20 +0300
Subject: [PATCH] #17572: Avoid chained exceptions while passing bad directives
 to time.strptime().  Initial patch by Claudiu Popa.

---
 Lib/_strptime.py          | 2 +-
 Lib/test/test_strptime.py | 6 ++++++
 Lib/test/test_time.py     | 6 ++++++
 Misc/NEWS                 | 3 +++
 4 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/Lib/_strptime.py b/Lib/_strptime.py
index b0cd3d619e1..b089b08541a 100644
--- a/Lib/_strptime.py
+++ b/Lib/_strptime.py
@@ -326,7 +326,7 @@ def _strptime(data_string, format="%a %b %d %H:%M:%S %Y"):
                     bad_directive = "%"
                 del err
                 raise ValueError("'%s' is a bad directive in format '%s'" %
-                                    (bad_directive, format))
+                                    (bad_directive, format)) from None
             # IndexError only occurs when the format string is "%"
             except IndexError:
                 raise ValueError("stray %% in format '%s'" % format)
diff --git a/Lib/test/test_strptime.py b/Lib/test/test_strptime.py
index 90aac5b3f67..68e6a676363 100644
--- a/Lib/test/test_strptime.py
+++ b/Lib/test/test_strptime.py
@@ -218,6 +218,12 @@ class StrptimeTests(unittest.TestCase):
             else:
                 self.fail("'%s' did not raise ValueError" % bad_format)
 
+    def test_strptime_exception_context(self):
+        # check that this doesn't chain exceptions needlessly (see #17572)
+        with self.assertRaises(ValueError) as e:
+            _strptime._strptime_time('', '%D')
+        self.assertIs(e.exception.__suppress_context__, True)
+
     def test_unconverteddata(self):
         # Check ValueError is raised when there is unconverted data
         self.assertRaises(ValueError, _strptime._strptime_time, "10 12", "%m")
diff --git a/Lib/test/test_time.py b/Lib/test/test_time.py
index da0f555d916..0e4d70284bf 100644
--- a/Lib/test/test_time.py
+++ b/Lib/test/test_time.py
@@ -193,6 +193,12 @@ class TimeTestCase(unittest.TestCase):
         self.assertRaises(TypeError, time.strptime, b'2009', "%Y")
         self.assertRaises(TypeError, time.strptime, '2009', b'%Y')
 
+    def test_strptime_exception_context(self):
+        # check that this doesn't chain exceptions needlessly (see #17572)
+        with self.assertRaises(ValueError) as e:
+            time.strptime('', '%D')
+        self.assertIs(e.exception.__suppress_context__, True)
+
     def test_asctime(self):
         time.asctime(time.gmtime(self.t))
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 03f9e2f8f7e..4405779a758 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -21,6 +21,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #17572: Avoid chained exceptions while passing bad directives to
+  time.strptime().  Initial patch by Claudiu Popa.
+
 - Issue #14254: IDLE now handles readline correctly across shell restarts.
 
 - Issue #17614: IDLE no longer raises exception when quickly closing a file.