Issue #19545: Avoid chained exceptions while passing stray % to

time.strptime().  Initial patch by Claudiu Popa.

3 files changed, 9 insertions, 1 deletions

diff --git a/Lib/_strptime.py b/Lib/_strptime.py
index 3884a67..d101c6d 100644
--- a/Lib/_strptime.py
+++ b/Lib/_strptime.py
@@ -329,7 +329,7 @@ def _strptime(data_string, format="%a %b %d %H:%M:%S %Y"):
                                     (bad_directive, format)) from None
             # IndexError only occurs when the format string is "%"
             except IndexError:
-                raise ValueError("stray %% in format '%s'" % format)
+                raise ValueError("stray %% in format '%s'" % format) from None
             _regex_cache[format] = format_regex
     found = format_regex.match(data_string)
     if not found:
diff --git a/Lib/test/test_strptime.py b/Lib/test/test_strptime.py
index 68e6a67..d5bc39d 100644
--- a/Lib/test/test_strptime.py
+++ b/Lib/test/test_strptime.py
@@ -223,6 +223,10 @@ class StrptimeTests(unittest.TestCase):
         with self.assertRaises(ValueError) as e:
             _strptime._strptime_time('', '%D')
         self.assertIs(e.exception.__suppress_context__, True)
+        # additional check for IndexError branch (issue #19545)
+        with self.assertRaises(ValueError) as e:
+            _strptime._strptime_time('19', '%Y %')
+        self.assertIs(e.exception.__suppress_context__, True)
 
     def test_unconverteddata(self):
         # Check ValueError is raised when there is unconverted data
diff --git a/Lib/test/test_time.py b/Lib/test/test_time.py
index f3643b6..44bcb94 100644
--- a/Lib/test/test_time.py
+++ b/Lib/test/test_time.py
@@ -198,6 +198,10 @@ class TimeTestCase(unittest.TestCase):
         with self.assertRaises(ValueError) as e:
             time.strptime('', '%D')
         self.assertIs(e.exception.__suppress_context__, True)
+        # additional check for IndexError branch (issue #19545)
+        with self.assertRaises(ValueError) as e:
+            time.strptime('19', '%Y %')
+        self.assertIs(e.exception.__suppress_context__, True)
 
     def test_asctime(self):
         time.asctime(time.gmtime(self.t))