GH-70647: Deprecate strptime day of month parsing without a year present to avoid leap-year bugs (GH-117107)

3 files changed, 31 insertions, 0 deletions

diff --git a/Lib/test/datetimetester.py b/Lib/test/datetimetester.py
index 31fc383..c772639 100644
--- a/Lib/test/datetimetester.py
+++ b/Lib/test/datetimetester.py
@@ -2793,6 +2793,19 @@ class TestDateTime(TestDate):
                 newdate = strptime(string, format)
                 self.assertEqual(newdate, target, msg=reason)
 
+    def test_strptime_leap_year(self):
+        # GH-70647: warns if parsing a format with a day and no year.
+        with self.assertRaises(ValueError):
+            # The existing behavior that GH-70647 seeks to change.
+            self.theclass.strptime('02-29', '%m-%d')
+        with self.assertWarnsRegex(DeprecationWarning,
+                                   r'.*day of month without a year.*'):
+            self.theclass.strptime('03-14.159265', '%m-%d.%f')
+        with self._assertNotWarns(DeprecationWarning):
+            self.theclass.strptime('20-03-14.159265', '%y-%m-%d.%f')
+        with self._assertNotWarns(DeprecationWarning):
+            self.theclass.strptime('02-29,2024', '%m-%d,%Y')
+
     def test_more_timetuple(self):
         # This tests fields beyond those tested by the TestDate.test_timetuple.
         t = self.theclass(2004, 12, 31, 6, 22, 33)
diff --git a/Lib/test/test_time.py b/Lib/test/test_time.py
index fb234b7..293799f 100644
--- a/Lib/test/test_time.py
+++ b/Lib/test/test_time.py
@@ -277,6 +277,8 @@ class TimeTestCase(unittest.TestCase):
                           'j', 'm', 'M', 'p', 'S',
                           'U', 'w', 'W', 'x', 'X', 'y', 'Y', 'Z', '%'):
             format = '%' + directive
+            if directive == 'd':
+                format += ',%Y'  # Avoid GH-70647.
             strf_output = time.strftime(format, tt)
             try:
                 time.strptime(strf_output, format)
@@ -299,6 +301,12 @@ class TimeTestCase(unittest.TestCase):
             time.strptime('19', '%Y %')
         self.assertIs(e.exception.__suppress_context__, True)
 
+    def test_strptime_leap_year(self):
+        # GH-70647: warns if parsing a format with a day and no year.
+        with self.assertWarnsRegex(DeprecationWarning,
+                                   r'.*day of month without a year.*'):
+            time.strptime('02-07 18:28', '%m-%d %H:%M')
+
     def test_asctime(self):
         time.asctime(time.gmtime(self.t))
 
diff --git a/Lib/test/test_unittest/test_assertions.py b/Lib/test/test_unittest/test_assertions.py
index 5c1a28e..1dec947 100644
--- a/Lib/test/test_unittest/test_assertions.py
+++ b/Lib/test/test_unittest/test_assertions.py
@@ -386,6 +386,16 @@ class TestLongMessage(unittest.TestCase):
                                '^UserWarning not triggered$',
                                '^UserWarning not triggered : oops$'])
 
+    def test_assertNotWarns(self):
+        def warn_future():
+            warnings.warn('xyz', FutureWarning, stacklevel=2)
+        self.assertMessagesCM('_assertNotWarns', (FutureWarning,),
+                              warn_future,
+                              ['^FutureWarning triggered$',
+                               '^oops$',
+                               '^FutureWarning triggered$',
+                               '^FutureWarning triggered : oops$'])
+
     def testAssertWarnsRegex(self):
         # test error not raised
         self.assertMessagesCM('assertWarnsRegex', (UserWarning, 'unused regex'),