Issue #14657: The frozen instance of importlib used for bootstrap is now also the module imported as importlib._bootstrap.

Lib/importlib/__init__.py

@@ -1,19 +1,26 @@
 """A pure Python implementation of import."""
 __all__ = ['__import__', 'import_module', 'invalidate_caches']
 
-from . import _bootstrap
-
-
-# To simplify imports in test code
-_w_long = _bootstrap._w_long
-_r_long = _bootstrap._r_long
-
-
 # Bootstrap help #####################################################
 import imp
 import sys
 
-_bootstrap._setup(sys, imp)
+try:
+    _bootstrap = sys.modules['_frozen_importlib']
+except ImportError:
+    from . import _bootstrap
+    _bootstrap._setup(sys, imp)
+else:
+    # importlib._bootstrap is the built-in import, ensure we don't create
+    # a second copy of the module.
+    _bootstrap.__name__ = 'importlib._bootstrap'
+    _bootstrap.__package__ = 'importlib'
+    _bootstrap.__file__ = __file__.replace('__init__.py', '_bootstrap.py')
+    sys.modules['importlib._bootstrap'] = _bootstrap
+
+# To simplify imports in test code
+_w_long = _bootstrap._w_long
+_r_long = _bootstrap._r_long
 
 
 # Public API #########################################################

Lib/test/test_import.py

@@ -19,7 +19,7 @@
 from test.support import (
     EnvironmentVarGuard, TESTFN, check_warnings, forget, is_jython,
     make_legacy_pyc, rmtree, run_unittest, swap_attr, swap_item, temp_umask,
-    unlink, unload, create_empty_file)
+    unlink, unload, create_empty_file, cpython_only)
 from test import script_helper
 
 
@@ -746,6 +746,23 @@ def tearDown(self):
         sys.path[:] = self.orig_sys_path
 
 
+@cpython_only
+class ImportlibBootstrapTests(unittest.TestCase):
+    # These tests check that importlib is bootstrapped.
+
+    def test_frozen_importlib(self):
+        mod = sys.modules['_frozen_importlib']
+        self.assertTrue(mod)
+
+    def test_frozen_importlib_is_bootstrap(self):
+        from importlib import _bootstrap
+        mod = sys.modules['_frozen_importlib']
+        self.assertIs(mod, _bootstrap)
+        self.assertEqual(mod.__name__, 'importlib._bootstrap')
+        self.assertEqual(mod.__package__, 'importlib')
+        self.assertTrue(mod.__file__.endswith('_bootstrap.py'), mod.__file__)
+
+
 def test_main(verbose=None):
     flag = importlib_util.using___import__
     try:
@@ -753,6 +770,7 @@ def test_main(verbose=None):
         run_unittest(ImportTests, PycacheTests,
                      PycRewritingTests, PathsTests, RelativeImportTests,
                      OverridingImportBuiltinTests,
+                     ImportlibBootstrapTests,
                      TestSymbolicallyLinkedPackage,
                      importlib_import_test_suite())
     finally:

Misc/NEWS

@@ -29,6 +29,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #14657: The frozen instance of importlib used for bootstrap is now
+  also the module imported as importlib._bootstrap.
+
 - Issue #14055: Add __sizeof__ support to _elementtree.
 
 - Issue #15054: A bug in tokenize.tokenize that caused string literals