Issue #19205: Don't import the 're' module in site and sysconfig module to

to speed up interpreter start.

Lib/test/test_site.py

@@ -420,5 +420,20 @@ class ImportSideEffectTests(unittest.TestCase):
         self.assertEqual(code, 200, msg="Can't find " + url)
 
 
+class StartupImportTests(unittest.TestCase):
+
+    def test_startup_imports(self):
+        # This tests checks which modules are loaded by Python when it
+        # initially starts upon startup.
+        args = [sys.executable, '-I', '-c',
+                'import sys; print(set(sys.modules))']
+        stdout = subprocess.check_output(args)
+        modules = eval(stdout.decode('utf-8'))
+        self.assertIn('site', modules)
+
+        re_mods = {'re', '_sre', 'sre_compile', 'sre_constants', 'sre_parse'}
+        self.assertFalse(modules.intersection(re_mods))
+
+
 if __name__ == "__main__":
     unittest.main()