gh-143959: Fix test_datetime if _datetime is unavailable (GH-145248)

Lib/test/datetimetester.py

@@ -48,7 +48,11 @@ import _strptime
 try:
     import _pydatetime
 except ImportError:
-    pass
+    _pydatetime = None
+try:
+    import _datetime
+except ImportError:
+    _datetime = None
 #
 
 pickle_loads = {pickle.loads, pickle._loads}

Lib/test/test_datetime.py

@@ -18,16 +18,19 @@ def load_tests(loader, tests, pattern):
     finally:
         # XXX: import_fresh_module() is supposed to leave sys.module cache untouched,
         # XXX: but it does not, so we have to cleanup ourselves.
-        for modname in ['datetime', '_datetime', '_strptime']:
+        for modname in ['datetime', '_datetime', '_pydatetime', '_strptime']:
             sys.modules.pop(modname, None)
 
     test_modules = [pure_tests, fast_tests]
     test_suffixes = ["_Pure", "_Fast"]
+
     # XXX(gb) First run all the _Pure tests, then all the _Fast tests.  You might
     # not believe this, but in spite of all the sys.modules trickery running a _Pure
     # test last will leave a mix of pure and native datetime stuff lying around.
     for module, suffix in zip(test_modules, test_suffixes):
         test_classes = []
+        if module is None:
+            continue
         for name, cls in module.__dict__.items():
             if not isinstance(cls, type):
                 continue
@@ -48,8 +51,8 @@ def load_tests(loader, tests, pattern):
                     cls_._save_sys_modules = sys.modules.copy()
                     sys.modules[TESTS] = module
                     sys.modules['datetime'] = module.datetime_module
-                    if hasattr(module, '_pydatetime'):
-                        sys.modules['_pydatetime'] = module._pydatetime
+                    sys.modules['_pydatetime'] = module._pydatetime
+                    sys.modules['_datetime'] = module._datetime
                     sys.modules['_strptime'] = module._strptime
                     super().setUpClass()