Issue #17636: Circular imports involving relative imports are now supported.

11 files changed, 1134 insertions, 0 deletions

diff --git a/Lib/test/test_import/__init__.py b/Lib/test/test_import/__init__.py
new file mode 100644
index 0000000..fd21fa2
--- /dev/null
+++ b/Lib/test/test_import/__init__.py
@@ -0,0 +1,1113 @@
+# We import importlib *ASAP* in order to test #15386
+import importlib
+import importlib.util
+from importlib._bootstrap import _get_sourcefile
+import builtins
+import marshal
+import os
+import platform
+import py_compile
+import random
+import stat
+import sys
+import unittest
+import unittest.mock as mock
+import textwrap
+import errno
+import shutil
+import contextlib
+
+import test.support
+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, cpython_only, TESTFN_UNENCODABLE)
+from test import script_helper
+
+
+skip_if_dont_write_bytecode = unittest.skipIf(
+        sys.dont_write_bytecode,
+        "test meaningful only when writing bytecode")
+
+def remove_files(name):
+    for f in (name + ".py",
+              name + ".pyc",
+              name + ".pyo",
+              name + ".pyw",
+              name + "$py.class"):
+        unlink(f)
+    rmtree('__pycache__')
+
+
+@contextlib.contextmanager
+def _ready_to_import(name=None, source=""):
+    # sets up a temporary directory and removes it
+    # creates the module file
+    # temporarily clears the module from sys.modules (if any)
+    # reverts or removes the module when cleaning up
+    name = name or "spam"
+    with script_helper.temp_dir() as tempdir:
+        path = script_helper.make_script(tempdir, name, source)
+        old_module = sys.modules.pop(name, None)
+        try:
+            sys.path.insert(0, tempdir)
+            yield name, path
+            sys.path.remove(tempdir)
+        finally:
+            if old_module is not None:
+                sys.modules[name] = old_module
+            elif name in sys.modules:
+                del sys.modules[name]
+
+
+class ImportTests(unittest.TestCase):
+
+    def setUp(self):
+        remove_files(TESTFN)
+        importlib.invalidate_caches()
+
+    def tearDown(self):
+        unload(TESTFN)
+
+    def test_case_sensitivity(self):
+        # Brief digression to test that import is case-sensitive:  if we got
+        # this far, we know for sure that "random" exists.
+        with self.assertRaises(ImportError):
+            import RAnDoM
+
+    def test_double_const(self):
+        # Another brief digression to test the accuracy of manifest float
+        # constants.
+        from test import double_const  # don't blink -- that *was* the test
+
+    def test_import(self):
+        def test_with_extension(ext):
+            # The extension is normally ".py", perhaps ".pyw".
+            source = TESTFN + ext
+            pyo = TESTFN + ".pyo"
+            if is_jython:
+                pyc = TESTFN + "$py.class"
+            else:
+                pyc = TESTFN + ".pyc"
+
+            with open(source, "w") as f:
+                print("# This tests Python's ability to import a",
+                      ext, "file.", file=f)
+                a = random.randrange(1000)
+                b = random.randrange(1000)
+                print("a =", a, file=f)
+                print("b =", b, file=f)
+
+            if TESTFN in sys.modules:
+                del sys.modules[TESTFN]
+            importlib.invalidate_caches()
+            try:
+                try:
+                    mod = __import__(TESTFN)
+                except ImportError as err:
+                    self.fail("import from %s failed: %s" % (ext, err))
+
+                self.assertEqual(mod.a, a,
+                    "module loaded (%s) but contents invalid" % mod)
+                self.assertEqual(mod.b, b,
+                    "module loaded (%s) but contents invalid" % mod)
+            finally:
+                forget(TESTFN)
+                unlink(source)
+                unlink(pyc)
+                unlink(pyo)
+
+        sys.path.insert(0, os.curdir)
+        try:
+            test_with_extension(".py")
+            if sys.platform.startswith("win"):
+                for ext in [".PY", ".Py", ".pY", ".pyw", ".PYW", ".pYw"]:
+                    test_with_extension(ext)
+        finally:
+            del sys.path[0]
+
+    def test_module_with_large_stack(self, module='longlist'):
+        # Regression test for http://bugs.python.org/issue561858.
+        filename = module + '.py'
+
+        # Create a file with a list of 65000 elements.
+        with open(filename, 'w') as f:
+            f.write('d = [\n')
+            for i in range(65000):
+                f.write('"",\n')
+            f.write(']')
+
+        try:
+            # Compile & remove .py file; we only need .pyc (or .pyo).
+            # Bytecode must be relocated from the PEP 3147 bytecode-only location.
+            py_compile.compile(filename)
+        finally:
+            unlink(filename)
+
+        # Need to be able to load from current dir.
+        sys.path.append('')
+        importlib.invalidate_caches()
+
+        namespace = {}
+        try:
+            make_legacy_pyc(filename)
+            # This used to crash.
+            exec('import ' + module, None, namespace)
+        finally:
+            # Cleanup.
+            del sys.path[-1]
+            unlink(filename + 'c')
+            unlink(filename + 'o')
+
+            # Remove references to the module (unload the module)
+            namespace.clear()
+            try:
+                del sys.modules[module]
+            except KeyError:
+                pass
+
+    def test_failing_import_sticks(self):
+        source = TESTFN + ".py"
+        with open(source, "w") as f:
+            print("a = 1/0", file=f)
+
+        # New in 2.4, we shouldn't be able to import that no matter how often
+        # we try.
+        sys.path.insert(0, os.curdir)
+        importlib.invalidate_caches()
+        if TESTFN in sys.modules:
+            del sys.modules[TESTFN]
+        try:
+            for i in [1, 2, 3]:
+                self.assertRaises(ZeroDivisionError, __import__, TESTFN)
+                self.assertNotIn(TESTFN, sys.modules,
+                                 "damaged module in sys.modules on %i try" % i)
+        finally:
+            del sys.path[0]
+            remove_files(TESTFN)
+
+    def test_import_name_binding(self):
+        # import x.y.z binds x in the current namespace
+        import test as x
+        import test.support
+        self.assertIs(x, test, x.__name__)
+        self.assertTrue(hasattr(test.support, "__file__"))
+
+        # import x.y.z as w binds z as w
+        import test.support as y
+        self.assertIs(y, test.support, y.__name__)
+
+    def test_failing_reload(self):
+        # A failing reload should leave the module object in sys.modules.
+        source = TESTFN + os.extsep + "py"
+        with open(source, "w") as f:
+            f.write("a = 1\nb=2\n")
+
+        sys.path.insert(0, os.curdir)
+        try:
+            mod = __import__(TESTFN)
+            self.assertIn(TESTFN, sys.modules)
+            self.assertEqual(mod.a, 1, "module has wrong attribute values")
+            self.assertEqual(mod.b, 2, "module has wrong attribute values")
+
+            # On WinXP, just replacing the .py file wasn't enough to
+            # convince reload() to reparse it.  Maybe the timestamp didn't
+            # move enough.  We force it to get reparsed by removing the
+            # compiled file too.
+            remove_files(TESTFN)
+
+            # Now damage the module.
+            with open(source, "w") as f:
+                f.write("a = 10\nb=20//0\n")
+
+            self.assertRaises(ZeroDivisionError, importlib.reload, mod)
+            # But we still expect the module to be in sys.modules.
+            mod = sys.modules.get(TESTFN)
+            self.assertIsNotNone(mod, "expected module to be in sys.modules")
+
+            # We should have replaced a w/ 10, but the old b value should
+            # stick.
+            self.assertEqual(mod.a, 10, "module has wrong attribute values")
+            self.assertEqual(mod.b, 2, "module has wrong attribute values")
+
+        finally:
+            del sys.path[0]
+            remove_files(TESTFN)
+            unload(TESTFN)
+
+    @skip_if_dont_write_bytecode
+    def test_file_to_source(self):
+        # check if __file__ points to the source file where available
+        source = TESTFN + ".py"
+        with open(source, "w") as f:
+            f.write("test = None\n")
+
+        sys.path.insert(0, os.curdir)
+        try:
+            mod = __import__(TESTFN)
+            self.assertTrue(mod.__file__.endswith('.py'))
+            os.remove(source)
+            del sys.modules[TESTFN]
+            make_legacy_pyc(source)
+            importlib.invalidate_caches()
+            mod = __import__(TESTFN)
+            base, ext = os.path.splitext(mod.__file__)
+            self.assertIn(ext, ('.pyc', '.pyo'))
+        finally:
+            del sys.path[0]
+            remove_files(TESTFN)
+            if TESTFN in sys.modules:
+                del sys.modules[TESTFN]
+
+    def test_import_by_filename(self):
+        path = os.path.abspath(TESTFN)
+        encoding = sys.getfilesystemencoding()
+        try:
+            path.encode(encoding)
+        except UnicodeEncodeError:
+            self.skipTest('path is not encodable to {}'.format(encoding))
+        with self.assertRaises(ImportError) as c:
+            __import__(path)
+
+    def test_import_in_del_does_not_crash(self):
+        # Issue 4236
+        testfn = script_helper.make_script('', TESTFN, textwrap.dedent("""\
+            import sys
+            class C:
+               def __del__(self):
+                  import importlib
+            sys.argv.insert(0, C())
+            """))
+        script_helper.assert_python_ok(testfn)
+
+    def test_timestamp_overflow(self):
+        # A modification timestamp larger than 2**32 should not be a problem
+        # when importing a module (issue #11235).
+        sys.path.insert(0, os.curdir)
+        try:
+            source = TESTFN + ".py"
+            compiled = importlib.util.cache_from_source(source)
+            with open(source, 'w') as f:
+                pass
+            try:
+                os.utime(source, (2 ** 33 - 5, 2 ** 33 - 5))
+            except OverflowError:
+                self.skipTest("cannot set modification time to large integer")
+            except OSError as e:
+                if e.errno != getattr(errno, 'EOVERFLOW', None):
+                    raise
+                self.skipTest("cannot set modification time to large integer ({})".format(e))
+            __import__(TESTFN)
+            # The pyc file was created.
+            os.stat(compiled)
+        finally:
+            del sys.path[0]
+            remove_files(TESTFN)
+
+    def test_bogus_fromlist(self):
+        try:
+            __import__('http', fromlist=['blah'])
+        except ImportError:
+            self.fail("fromlist must allow bogus names")
+
+    @cpython_only
+    def test_delete_builtins_import(self):
+        args = ["-c", "del __builtins__.__import__; import os"]
+        popen = script_helper.spawn_python(*args)
+        stdout, stderr = popen.communicate()
+        self.assertIn(b"ImportError", stdout)
+
+    def test_from_import_message_for_nonexistent_module(self):
+        with self.assertRaisesRegex(ImportError, "^No module named 'bogus'"):
+            from bogus import foo
+
+    def test_from_import_message_for_existing_module(self):
+        with self.assertRaisesRegex(ImportError, "^cannot import name 'bogus'"):
+            from re import bogus
+
+
+@skip_if_dont_write_bytecode
+class FilePermissionTests(unittest.TestCase):
+    # tests for file mode on cached .pyc/.pyo files
+
+    @unittest.skipUnless(os.name == 'posix',
+                         "test meaningful only on posix systems")
+    def test_creation_mode(self):
+        mask = 0o022
+        with temp_umask(mask), _ready_to_import() as (name, path):
+            cached_path = importlib.util.cache_from_source(path)
+            module = __import__(name)
+            if not os.path.exists(cached_path):
+                self.fail("__import__ did not result in creation of "
+                          "either a .pyc or .pyo file")
+            stat_info = os.stat(cached_path)
+
+        # Check that the umask is respected, and the executable bits
+        # aren't set.
+        self.assertEqual(oct(stat.S_IMODE(stat_info.st_mode)),
+                         oct(0o666 & ~mask))
+
+    @unittest.skipUnless(os.name == 'posix',
+                         "test meaningful only on posix systems")
+    def test_cached_mode_issue_2051(self):
+        # permissions of .pyc should match those of .py, regardless of mask
+        mode = 0o600
+        with temp_umask(0o022), _ready_to_import() as (name, path):
+            cached_path = importlib.util.cache_from_source(path)
+            os.chmod(path, mode)
+            __import__(name)
+            if not os.path.exists(cached_path):
+                self.fail("__import__ did not result in creation of "
+                          "either a .pyc or .pyo file")
+            stat_info = os.stat(cached_path)
+
+        self.assertEqual(oct(stat.S_IMODE(stat_info.st_mode)), oct(mode))
+
+    @unittest.skipUnless(os.name == 'posix',
+                         "test meaningful only on posix systems")
+    def test_cached_readonly(self):
+        mode = 0o400
+        with temp_umask(0o022), _ready_to_import() as (name, path):
+            cached_path = importlib.util.cache_from_source(path)
+            os.chmod(path, mode)
+            __import__(name)
+            if not os.path.exists(cached_path):
+                self.fail("__import__ did not result in creation of "
+                          "either a .pyc or .pyo file")
+            stat_info = os.stat(cached_path)
+
+        expected = mode | 0o200 # Account for fix for issue #6074
+        self.assertEqual(oct(stat.S_IMODE(stat_info.st_mode)), oct(expected))
+
+    def test_pyc_always_writable(self):
+        # Initially read-only .pyc files on Windows used to cause problems
+        # with later updates, see issue #6074 for details
+        with _ready_to_import() as (name, path):
+            # Write a Python file, make it read-only and import it
+            with open(path, 'w') as f:
+                f.write("x = 'original'\n")
+            # Tweak the mtime of the source to ensure pyc gets updated later
+            s = os.stat(path)
+            os.utime(path, (s.st_atime, s.st_mtime-100000000))
+            os.chmod(path, 0o400)
+            m = __import__(name)
+            self.assertEqual(m.x, 'original')
+            # Change the file and then reimport it
+            os.chmod(path, 0o600)
+            with open(path, 'w') as f:
+                f.write("x = 'rewritten'\n")
+            unload(name)
+            importlib.invalidate_caches()
+            m = __import__(name)
+            self.assertEqual(m.x, 'rewritten')
+            # Now delete the source file and check the pyc was rewritten
+            unlink(path)
+            unload(name)
+            importlib.invalidate_caches()
+            if __debug__:
+                bytecode_only = path + "c"
+            else:
+                bytecode_only = path + "o"
+            os.rename(importlib.util.cache_from_source(path), bytecode_only)
+            m = __import__(name)
+            self.assertEqual(m.x, 'rewritten')
+
+
+class PycRewritingTests(unittest.TestCase):
+    # Test that the `co_filename` attribute on code objects always points
+    # to the right file, even when various things happen (e.g. both the .py
+    # and the .pyc file are renamed).
+
+    module_name = "unlikely_module_name"
+    module_source = """
+import sys
+code_filename = sys._getframe().f_code.co_filename
+module_filename = __file__
+constant = 1
+def func():
+    pass
+func_filename = func.__code__.co_filename
+"""
+    dir_name = os.path.abspath(TESTFN)
+    file_name = os.path.join(dir_name, module_name) + os.extsep + "py"
+    compiled_name = importlib.util.cache_from_source(file_name)
+
+    def setUp(self):
+        self.sys_path = sys.path[:]
+        self.orig_module = sys.modules.pop(self.module_name, None)
+        os.mkdir(self.dir_name)
+        with open(self.file_name, "w") as f:
+            f.write(self.module_source)
+        sys.path.insert(0, self.dir_name)
+        importlib.invalidate_caches()
+
+    def tearDown(self):
+        sys.path[:] = self.sys_path
+        if self.orig_module is not None:
+            sys.modules[self.module_name] = self.orig_module
+        else:
+            unload(self.module_name)
+        unlink(self.file_name)
+        unlink(self.compiled_name)
+        rmtree(self.dir_name)
+
+    def import_module(self):
+        ns = globals()
+        __import__(self.module_name, ns, ns)
+        return sys.modules[self.module_name]
+
+    def test_basics(self):
+        mod = self.import_module()
+        self.assertEqual(mod.module_filename, self.file_name)
+        self.assertEqual(mod.code_filename, self.file_name)
+        self.assertEqual(mod.func_filename, self.file_name)
+        del sys.modules[self.module_name]
+        mod = self.import_module()
+        self.assertEqual(mod.module_filename, self.file_name)
+        self.assertEqual(mod.code_filename, self.file_name)
+        self.assertEqual(mod.func_filename, self.file_name)
+
+    def test_incorrect_code_name(self):
+        py_compile.compile(self.file_name, dfile="another_module.py")
+        mod = self.import_module()
+        self.assertEqual(mod.module_filename, self.file_name)
+        self.assertEqual(mod.code_filename, self.file_name)
+        self.assertEqual(mod.func_filename, self.file_name)
+
+    def test_module_without_source(self):
+        target = "another_module.py"
+        py_compile.compile(self.file_name, dfile=target)
+        os.remove(self.file_name)
+        pyc_file = make_legacy_pyc(self.file_name)
+        importlib.invalidate_caches()
+        mod = self.import_module()
+        self.assertEqual(mod.module_filename, pyc_file)
+        self.assertEqual(mod.code_filename, target)
+        self.assertEqual(mod.func_filename, target)
+
+    def test_foreign_code(self):
+        py_compile.compile(self.file_name)
+        with open(self.compiled_name, "rb") as f:
+            header = f.read(12)
+            code = marshal.load(f)
+        constants = list(code.co_consts)
+        foreign_code = importlib.import_module.__code__
+        pos = constants.index(1)
+        constants[pos] = foreign_code
+        code = type(code)(code.co_argcount, code.co_kwonlyargcount,
+                          code.co_nlocals, code.co_stacksize,
+                          code.co_flags, code.co_code, tuple(constants),
+                          code.co_names, code.co_varnames, code.co_filename,
+                          code.co_name, code.co_firstlineno, code.co_lnotab,
+                          code.co_freevars, code.co_cellvars)
+        with open(self.compiled_name, "wb") as f:
+            f.write(header)
+            marshal.dump(code, f)
+        mod = self.import_module()
+        self.assertEqual(mod.constant.co_filename, foreign_code.co_filename)
+
+
+class PathsTests(unittest.TestCase):
+    SAMPLES = ('test', 'test\u00e4\u00f6\u00fc\u00df', 'test\u00e9\u00e8',
+               'test\u00b0\u00b3\u00b2')
+    path = TESTFN
+
+    def setUp(self):
+        os.mkdir(self.path)
+        self.syspath = sys.path[:]
+
+    def tearDown(self):
+        rmtree(self.path)
+        sys.path[:] = self.syspath
+
+    # Regression test for http://bugs.python.org/issue1293.
+    def test_trailing_slash(self):
+        with open(os.path.join(self.path, 'test_trailing_slash.py'), 'w') as f:
+            f.write("testdata = 'test_trailing_slash'")
+        sys.path.append(self.path+'/')
+        mod = __import__("test_trailing_slash")
+        self.assertEqual(mod.testdata, 'test_trailing_slash')
+        unload("test_trailing_slash")
+
+    # Regression test for http://bugs.python.org/issue3677.
+    @unittest.skipUnless(sys.platform == 'win32', 'Windows-specific')
+    def test_UNC_path(self):
+        with open(os.path.join(self.path, 'test_unc_path.py'), 'w') as f:
+            f.write("testdata = 'test_unc_path'")
+        importlib.invalidate_caches()
+        # Create the UNC path, like \\myhost\c$\foo\bar.
+        path = os.path.abspath(self.path)
+        import socket
+        hn = socket.gethostname()
+        drive = path[0]
+        unc = "\\\\%s\\%s$"%(hn, drive)
+        unc += path[2:]
+        try:
+            os.listdir(unc)
+        except OSError as e:
+            if e.errno in (errno.EPERM, errno.EACCES):
+                # See issue #15338
+                self.skipTest("cannot access administrative share %r" % (unc,))
+            raise
+        sys.path.insert(0, unc)
+        try:
+            mod = __import__("test_unc_path")
+        except ImportError as e:
+            self.fail("could not import 'test_unc_path' from %r: %r"
+                      % (unc, e))
+        self.assertEqual(mod.testdata, 'test_unc_path')
+        self.assertTrue(mod.__file__.startswith(unc), mod.__file__)
+        unload("test_unc_path")
+
+
+class RelativeImportTests(unittest.TestCase):
+
+    def tearDown(self):
+        unload("test.relimport")
+    setUp = tearDown
+
+    def test_relimport_star(self):
+        # This will import * from .test_import.
+        from .. import relimport
+        self.assertTrue(hasattr(relimport, "RelativeImportTests"))
+
+    def test_issue3221(self):
+        # Note for mergers: the 'absolute' tests from the 2.x branch
+        # are missing in Py3k because implicit relative imports are
+        # a thing of the past
+        #
+        # Regression test for http://bugs.python.org/issue3221.
+        def check_relative():
+            exec("from . import relimport", ns)
+
+        # Check relative import OK with __package__ and __name__ correct
+        ns = dict(__package__='test', __name__='test.notarealmodule')
+        check_relative()
+
+        # Check relative import OK with only __name__ wrong
+        ns = dict(__package__='test', __name__='notarealpkg.notarealmodule')
+        check_relative()
+
+        # Check relative import fails with only __package__ wrong
+        ns = dict(__package__='foo', __name__='test.notarealmodule')
+        self.assertRaises(SystemError, check_relative)
+
+        # Check relative import fails with __package__ and __name__ wrong
+        ns = dict(__package__='foo', __name__='notarealpkg.notarealmodule')
+        self.assertRaises(SystemError, check_relative)
+
+        # Check relative import fails with package set to a non-string
+        ns = dict(__package__=object())
+        self.assertRaises(TypeError, check_relative)
+
+    def test_absolute_import_without_future(self):
+        # If explicit relative import syntax is used, then do not try
+        # to perform an absolute import in the face of failure.
+        # Issue #7902.
+        with self.assertRaises(ImportError):
+            from .os import sep
+            self.fail("explicit relative import triggered an "
+                      "implicit absolute import")
+
+
+class OverridingImportBuiltinTests(unittest.TestCase):
+    def test_override_builtin(self):
+        # Test that overriding builtins.__import__ can bypass sys.modules.
+        import os
+
+        def foo():
+            import os
+            return os
+        self.assertEqual(foo(), os)  # Quick sanity check.
+
+        with swap_attr(builtins, "__import__", lambda *x: 5):
+            self.assertEqual(foo(), 5)
+
+        # Test what happens when we shadow __import__ in globals(); this
+        # currently does not impact the import process, but if this changes,
+        # other code will need to change, so keep this test as a tripwire.
+        with swap_item(globals(), "__import__", lambda *x: 5):
+            self.assertEqual(foo(), os)
+
+
+class PycacheTests(unittest.TestCase):
+    # Test the various PEP 3147 related behaviors.
+
+    tag = sys.implementation.cache_tag
+
+    def _clean(self):
+        forget(TESTFN)
+        rmtree('__pycache__')
+        unlink(self.source)
+
+    def setUp(self):
+        self.source = TESTFN + '.py'
+        self._clean()
+        with open(self.source, 'w') as fp:
+            print('# This is a test file written by test_import.py', file=fp)
+        sys.path.insert(0, os.curdir)
+        importlib.invalidate_caches()
+
+    def tearDown(self):
+        assert sys.path[0] == os.curdir, 'Unexpected sys.path[0]'
+        del sys.path[0]
+        self._clean()
+
+    @skip_if_dont_write_bytecode
+    def test_import_pyc_path(self):
+        self.assertFalse(os.path.exists('__pycache__'))
+        __import__(TESTFN)
+        self.assertTrue(os.path.exists('__pycache__'))
+        self.assertTrue(os.path.exists(os.path.join(
+            '__pycache__', '{}.{}.py{}'.format(
+            TESTFN, self.tag, 'c' if __debug__ else 'o'))))
+
+    @unittest.skipUnless(os.name == 'posix',
+                         "test meaningful only on posix systems")
+    @unittest.skipIf(hasattr(os, 'geteuid') and os.geteuid() == 0,
+            "due to varying filesystem permission semantics (issue #11956)")
+    @skip_if_dont_write_bytecode
+    def test_unwritable_directory(self):
+        # When the umask causes the new __pycache__ directory to be
+        # unwritable, the import still succeeds but no .pyc file is written.
+        with temp_umask(0o222):
+            __import__(TESTFN)
+        self.assertTrue(os.path.exists('__pycache__'))
+        self.assertFalse(os.path.exists(os.path.join(
+            '__pycache__', '{}.{}.pyc'.format(TESTFN, self.tag))))
+
+    @skip_if_dont_write_bytecode
+    def test_missing_source(self):
+        # With PEP 3147 cache layout, removing the source but leaving the pyc
+        # file does not satisfy the import.
+        __import__(TESTFN)
+        pyc_file = importlib.util.cache_from_source(self.source)
+        self.assertTrue(os.path.exists(pyc_file))
+        os.remove(self.source)
+        forget(TESTFN)
+        importlib.invalidate_caches()
+        self.assertRaises(ImportError, __import__, TESTFN)
+
+    @skip_if_dont_write_bytecode
+    def test_missing_source_legacy(self):
+        # Like test_missing_source() except that for backward compatibility,
+        # when the pyc file lives where the py file would have been (and named
+        # without the tag), it is importable.  The __file__ of the imported
+        # module is the pyc location.
+        __import__(TESTFN)
+        # pyc_file gets removed in _clean() via tearDown().
+        pyc_file = make_legacy_pyc(self.source)
+        os.remove(self.source)
+        unload(TESTFN)
+        importlib.invalidate_caches()
+        m = __import__(TESTFN)
+        self.assertEqual(m.__file__,
+                         os.path.join(os.curdir, os.path.relpath(pyc_file)))
+
+    def test___cached__(self):
+        # Modules now also have an __cached__ that points to the pyc file.
+        m = __import__(TESTFN)
+        pyc_file = importlib.util.cache_from_source(TESTFN + '.py')
+        self.assertEqual(m.__cached__, os.path.join(os.curdir, pyc_file))
+
+    @skip_if_dont_write_bytecode
+    def test___cached___legacy_pyc(self):
+        # Like test___cached__() except that for backward compatibility,
+        # when the pyc file lives where the py file would have been (and named
+        # without the tag), it is importable.  The __cached__ of the imported
+        # module is the pyc location.
+        __import__(TESTFN)
+        # pyc_file gets removed in _clean() via tearDown().
+        pyc_file = make_legacy_pyc(self.source)
+        os.remove(self.source)
+        unload(TESTFN)
+        importlib.invalidate_caches()
+        m = __import__(TESTFN)
+        self.assertEqual(m.__cached__,
+                         os.path.join(os.curdir, os.path.relpath(pyc_file)))
+
+    @skip_if_dont_write_bytecode
+    def test_package___cached__(self):
+        # Like test___cached__ but for packages.
+        def cleanup():
+            rmtree('pep3147')
+            unload('pep3147.foo')
+            unload('pep3147')
+        os.mkdir('pep3147')
+        self.addCleanup(cleanup)
+        # Touch the __init__.py
+        with open(os.path.join('pep3147', '__init__.py'), 'w'):
+            pass
+        with open(os.path.join('pep3147', 'foo.py'), 'w'):
+            pass
+        importlib.invalidate_caches()
+        m = __import__('pep3147.foo')
+        init_pyc = importlib.util.cache_from_source(
+            os.path.join('pep3147', '__init__.py'))
+        self.assertEqual(m.__cached__, os.path.join(os.curdir, init_pyc))
+        foo_pyc = importlib.util.cache_from_source(os.path.join('pep3147', 'foo.py'))
+        self.assertEqual(sys.modules['pep3147.foo'].__cached__,
+                         os.path.join(os.curdir, foo_pyc))
+
+    def test_package___cached___from_pyc(self):
+        # Like test___cached__ but ensuring __cached__ when imported from a
+        # PEP 3147 pyc file.
+        def cleanup():
+            rmtree('pep3147')
+            unload('pep3147.foo')
+            unload('pep3147')
+        os.mkdir('pep3147')
+        self.addCleanup(cleanup)
+        # Touch the __init__.py
+        with open(os.path.join('pep3147', '__init__.py'), 'w'):
+            pass
+        with open(os.path.join('pep3147', 'foo.py'), 'w'):
+            pass
+        importlib.invalidate_caches()
+        m = __import__('pep3147.foo')
+        unload('pep3147.foo')
+        unload('pep3147')
+        importlib.invalidate_caches()
+        m = __import__('pep3147.foo')
+        init_pyc = importlib.util.cache_from_source(
+            os.path.join('pep3147', '__init__.py'))
+        self.assertEqual(m.__cached__, os.path.join(os.curdir, init_pyc))
+        foo_pyc = importlib.util.cache_from_source(os.path.join('pep3147', 'foo.py'))
+        self.assertEqual(sys.modules['pep3147.foo'].__cached__,
+                         os.path.join(os.curdir, foo_pyc))
+
+    def test_recompute_pyc_same_second(self):
+        # Even when the source file doesn't change timestamp, a change in
+        # source size is enough to trigger recomputation of the pyc file.
+        __import__(TESTFN)
+        unload(TESTFN)
+        with open(self.source, 'a') as fp:
+            print("x = 5", file=fp)
+        m = __import__(TESTFN)
+        self.assertEqual(m.x, 5)
+
+
+class TestSymbolicallyLinkedPackage(unittest.TestCase):
+    package_name = 'sample'
+    tagged = package_name + '-tagged'
+
+    def setUp(self):
+        test.support.rmtree(self.tagged)
+        test.support.rmtree(self.package_name)
+        self.orig_sys_path = sys.path[:]
+
+        # create a sample package; imagine you have a package with a tag and
+        #  you want to symbolically link it from its untagged name.
+        os.mkdir(self.tagged)
+        self.addCleanup(test.support.rmtree, self.tagged)
+        init_file = os.path.join(self.tagged, '__init__.py')
+        test.support.create_empty_file(init_file)
+        assert os.path.exists(init_file)
+
+        # now create a symlink to the tagged package
+        # sample -> sample-tagged
+        os.symlink(self.tagged, self.package_name, target_is_directory=True)
+        self.addCleanup(test.support.unlink, self.package_name)
+        importlib.invalidate_caches()
+
+        self.assertEqual(os.path.isdir(self.package_name), True)
+
+        assert os.path.isfile(os.path.join(self.package_name, '__init__.py'))
+
+    def tearDown(self):
+        sys.path[:] = self.orig_sys_path
+
+    # regression test for issue6727
+    @unittest.skipUnless(
+        not hasattr(sys, 'getwindowsversion')
+        or sys.getwindowsversion() >= (6, 0),
+        "Windows Vista or later required")
+    @test.support.skip_unless_symlink
+    def test_symlinked_dir_importable(self):
+        # make sure sample can only be imported from the current directory.
+        sys.path[:] = ['.']
+        assert os.path.exists(self.package_name)
+        assert os.path.exists(os.path.join(self.package_name, '__init__.py'))
+
+        # Try to import the package
+        importlib.import_module(self.package_name)
+
+
+@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_there_can_be_only_one(self):
+        # Issue #15386 revealed a tricky loophole in the bootstrapping
+        # This test is technically redundant, since the bug caused importing
+        # this test module to crash completely, but it helps prove the point
+        from importlib import machinery
+        mod = sys.modules['_frozen_importlib']
+        self.assertIs(machinery.FileFinder, mod.FileFinder)
+
+
+@cpython_only
+class GetSourcefileTests(unittest.TestCase):
+
+    """Test importlib._bootstrap._get_sourcefile() as used by the C API.
+
+    Because of the peculiarities of the need of this function, the tests are
+    knowingly whitebox tests.
+
+    """
+
+    def test_get_sourcefile(self):
+        # Given a valid bytecode path, return the path to the corresponding
+        # source file if it exists.
+        with mock.patch('importlib._bootstrap._path_isfile') as _path_isfile:
+            _path_isfile.return_value = True;
+            path = TESTFN + '.pyc'
+            expect = TESTFN + '.py'
+            self.assertEqual(_get_sourcefile(path), expect)
+
+    def test_get_sourcefile_no_source(self):
+        # Given a valid bytecode path without a corresponding source path,
+        # return the original bytecode path.
+        with mock.patch('importlib._bootstrap._path_isfile') as _path_isfile:
+            _path_isfile.return_value = False;
+            path = TESTFN + '.pyc'
+            self.assertEqual(_get_sourcefile(path), path)
+
+    def test_get_sourcefile_bad_ext(self):
+        # Given a path with an invalid bytecode extension, return the
+        # bytecode path passed as the argument.
+        path = TESTFN + '.bad_ext'
+        self.assertEqual(_get_sourcefile(path), path)
+
+
+class ImportTracebackTests(unittest.TestCase):
+
+    def setUp(self):
+        os.mkdir(TESTFN)
+        self.old_path = sys.path[:]
+        sys.path.insert(0, TESTFN)
+
+    def tearDown(self):
+        sys.path[:] = self.old_path
+        rmtree(TESTFN)
+
+    def create_module(self, mod, contents, ext=".py"):
+        fname = os.path.join(TESTFN, mod + ext)
+        with open(fname, "w") as f:
+            f.write(contents)
+        self.addCleanup(unload, mod)
+        importlib.invalidate_caches()
+        return fname
+
+    def assert_traceback(self, tb, files):
+        deduped_files = []
+        while tb:
+            code = tb.tb_frame.f_code
+            fn = code.co_filename
+            if not deduped_files or fn != deduped_files[-1]:
+                deduped_files.append(fn)
+            tb = tb.tb_next
+        self.assertEqual(len(deduped_files), len(files), deduped_files)
+        for fn, pat in zip(deduped_files, files):
+            self.assertIn(pat, fn)
+
+    def test_nonexistent_module(self):
+        try:
+            # assertRaises() clears __traceback__
+            import nonexistent_xyzzy
+        except ImportError as e:
+            tb = e.__traceback__
+        else:
+            self.fail("ImportError should have been raised")
+        self.assert_traceback(tb, [__file__])
+
+    def test_nonexistent_module_nested(self):
+        self.create_module("foo", "import nonexistent_xyzzy")
+        try:
+            import foo
+        except ImportError as e:
+            tb = e.__traceback__
+        else:
+            self.fail("ImportError should have been raised")
+        self.assert_traceback(tb, [__file__, 'foo.py'])
+
+    def test_exec_failure(self):
+        self.create_module("foo", "1/0")
+        try:
+            import foo
+        except ZeroDivisionError as e:
+            tb = e.__traceback__
+        else:
+            self.fail("ZeroDivisionError should have been raised")
+        self.assert_traceback(tb, [__file__, 'foo.py'])
+
+    def test_exec_failure_nested(self):
+        self.create_module("foo", "import bar")
+        self.create_module("bar", "1/0")
+        try:
+            import foo
+        except ZeroDivisionError as e:
+            tb = e.__traceback__
+        else:
+            self.fail("ZeroDivisionError should have been raised")
+        self.assert_traceback(tb, [__file__, 'foo.py', 'bar.py'])
+
+    # A few more examples from issue #15425
+    def test_syntax_error(self):
+        self.create_module("foo", "invalid syntax is invalid")
+        try:
+            import foo
+        except SyntaxError as e:
+            tb = e.__traceback__
+        else:
+            self.fail("SyntaxError should have been raised")
+        self.assert_traceback(tb, [__file__])
+
+    def _setup_broken_package(self, parent, child):
+        pkg_name = "_parent_foo"
+        self.addCleanup(unload, pkg_name)
+        pkg_path = os.path.join(TESTFN, pkg_name)
+        os.mkdir(pkg_path)
+        # Touch the __init__.py
+        init_path = os.path.join(pkg_path, '__init__.py')
+        with open(init_path, 'w') as f:
+            f.write(parent)
+        bar_path = os.path.join(pkg_path, 'bar.py')
+        with open(bar_path, 'w') as f:
+            f.write(child)
+        importlib.invalidate_caches()
+        return init_path, bar_path
+
+    def test_broken_submodule(self):
+        init_path, bar_path = self._setup_broken_package("", "1/0")
+        try:
+            import _parent_foo.bar
+        except ZeroDivisionError as e:
+            tb = e.__traceback__
+        else:
+            self.fail("ZeroDivisionError should have been raised")
+        self.assert_traceback(tb, [__file__, bar_path])
+
+    def test_broken_from(self):
+        init_path, bar_path = self._setup_broken_package("", "1/0")
+        try:
+            from _parent_foo import bar
+        except ZeroDivisionError as e:
+            tb = e.__traceback__
+        else:
+            self.fail("ImportError should have been raised")
+        self.assert_traceback(tb, [__file__, bar_path])
+
+    def test_broken_parent(self):
+        init_path, bar_path = self._setup_broken_package("1/0", "")
+        try:
+            import _parent_foo.bar
+        except ZeroDivisionError as e:
+            tb = e.__traceback__
+        else:
+            self.fail("ZeroDivisionError should have been raised")
+        self.assert_traceback(tb, [__file__, init_path])
+
+    def test_broken_parent_from(self):
+        init_path, bar_path = self._setup_broken_package("1/0", "")
+        try:
+            from _parent_foo import bar
+        except ZeroDivisionError as e:
+            tb = e.__traceback__
+        else:
+            self.fail("ZeroDivisionError should have been raised")
+        self.assert_traceback(tb, [__file__, init_path])
+
+    @cpython_only
+    def test_import_bug(self):
+        # We simulate a bug in importlib and check that it's not stripped
+        # away from the traceback.
+        self.create_module("foo", "")
+        importlib = sys.modules['_frozen_importlib']
+        if 'load_module' in vars(importlib.SourceLoader):
+            old_exec_module = importlib.SourceLoader.exec_module
+        else:
+            old_exec_module = None
+        try:
+            def exec_module(*args):
+                1/0
+            importlib.SourceLoader.exec_module = exec_module
+            try:
+                import foo
+            except ZeroDivisionError as e:
+                tb = e.__traceback__
+            else:
+                self.fail("ZeroDivisionError should have been raised")
+            self.assert_traceback(tb, [__file__, '<frozen importlib', __file__])
+        finally:
+            if old_exec_module is None:
+                del importlib.SourceLoader.exec_module
+            else:
+                importlib.SourceLoader.exec_module = old_exec_module
+
+    @unittest.skipUnless(TESTFN_UNENCODABLE, 'need TESTFN_UNENCODABLE')
+    def test_unencodable_filename(self):
+        # Issue #11619: The Python parser and the import machinery must not
+        # encode filenames, especially on Windows
+        pyname = script_helper.make_script('', TESTFN_UNENCODABLE, 'pass')
+        self.addCleanup(unlink, pyname)
+        name = pyname[:-3]
+        script_helper.assert_python_ok("-c", "mod = __import__(%a)" % name,
+                                       __isolated=False)
+
+
+class CircularImportTests(unittest.TestCase):
+
+    """See the docstrings of the modules being imported for the purpose of the
+    test."""
+
+    def tearDown(self):
+        """Make sure no modules pre-exist in sys.modules which are being used to
+        test."""
+        for key in list(sys.modules.keys()):
+            if key.startswith('test.test_import.data.circular_imports'):
+                del sys.modules[key]
+
+    def test_direct(self):
+        try:
+            import test.test_import.data.circular_imports.basic
+        except ImportError:
+            self.fail('circular import through relative imports failed')
+
+    def test_indirect(self):
+        try:
+            import test.test_import.data.circular_imports.indirect
+        except ImportError:
+            self.fail('relative import in module contributing to circular '
+                      'import failed')
+
+    def test_subpackage(self):
+        try:
+            import test.test_import.data.circular_imports.subpackage
+        except ImportError:
+            self.fail('circular import involving a subpackage failed')
+
+    def test_rebinding(self):
+        try:
+            import test.test_import.data.circular_imports.rebinding as rebinding
+        except ImportError:
+            self.fail('circular import with rebinding of module attribute failed')
+        from test.test_import.data.circular_imports.subpkg import util
+        self.assertIs(util.util, rebinding.util)
+
+
+if __name__ == '__main__':
+    # Test needs to be a package, so we can do relative imports.
+    unittest.main()
diff --git a/Lib/test/test_import/__main__.py b/Lib/test/test_import/__main__.py
new file mode 100644
index 0000000..ce26cbd
--- /dev/null
+++ b/Lib/test/test_import/__main__.py
@@ -0,0 +1,3 @@
+import unittest
+
+unittest.main('test.test_import')
\ No newline at end of file
diff --git a/Lib/test/test_import/data/circular_imports/basic.py b/Lib/test/test_import/data/circular_imports/basic.py
new file mode 100644
index 0000000..3e41e39
--- /dev/null
+++ b/Lib/test/test_import/data/circular_imports/basic.py
@@ -0,0 +1,2 @@
+"""Circular imports through direct, relative imports."""
+from . import basic2
diff --git a/Lib/test/test_import/data/circular_imports/basic2.py b/Lib/test/test_import/data/circular_imports/basic2.py
new file mode 100644
index 0000000..00bd2f2
--- /dev/null
+++ b/Lib/test/test_import/data/circular_imports/basic2.py
@@ -0,0 +1 @@
+from . import basic
diff --git a/Lib/test/test_import/data/circular_imports/indirect.py b/Lib/test/test_import/data/circular_imports/indirect.py
new file mode 100644
index 0000000..6925788
--- /dev/null
+++ b/Lib/test/test_import/data/circular_imports/indirect.py
@@ -0,0 +1 @@
+from . import basic, basic2
diff --git a/Lib/test/test_import/data/circular_imports/rebinding.py b/Lib/test/test_import/data/circular_imports/rebinding.py
new file mode 100644
index 0000000..f51d1c6
--- /dev/null
+++ b/Lib/test/test_import/data/circular_imports/rebinding.py
@@ -0,0 +1,3 @@
+"""Test the binding of names when a circular import shares the same name as an
+attribute."""
+from .rebinding2 import util
\ No newline at end of file
diff --git a/Lib/test/test_import/data/circular_imports/rebinding2.py b/Lib/test/test_import/data/circular_imports/rebinding2.py
new file mode 100644
index 0000000..62ca726
--- /dev/null
+++ b/Lib/test/test_import/data/circular_imports/rebinding2.py
@@ -0,0 +1,3 @@
+from .subpkg import util
+from . import rebinding
+util = util.util
\ No newline at end of file
diff --git a/Lib/test/test_import/data/circular_imports/subpackage.py b/Lib/test/test_import/data/circular_imports/subpackage.py
new file mode 100644
index 0000000..cc36c3c
--- /dev/null
+++ b/Lib/test/test_import/data/circular_imports/subpackage.py
@@ -0,0 +1,2 @@
+"""Circular import involving a sub-package."""
+from .subpkg import subpackage2
\ No newline at end of file
diff --git a/Lib/test/test_import/data/circular_imports/subpkg/subpackage2.py b/Lib/test/test_import/data/circular_imports/subpkg/subpackage2.py
new file mode 100644
index 0000000..07e0bc0
--- /dev/null
+++ b/Lib/test/test_import/data/circular_imports/subpkg/subpackage2.py
@@ -0,0 +1,2 @@
+#from .util import util
+from .. import subpackage
\ No newline at end of file
diff --git a/Lib/test/test_import/data/circular_imports/subpkg/util.py b/Lib/test/test_import/data/circular_imports/subpkg/util.py
new file mode 100644
index 0000000..f1505e9
--- /dev/null
+++ b/Lib/test/test_import/data/circular_imports/subpkg/util.py
@@ -0,0 +1,2 @@
+def util():
+    pass
\ No newline at end of file
diff --git a/Lib/test/test_import/data/circular_imports/util.py b/Lib/test/test_import/data/circular_imports/util.py
new file mode 100644
index 0000000..f1505e9
--- /dev/null
+++ b/Lib/test/test_import/data/circular_imports/util.py
@@ -0,0 +1,2 @@
+def util():
+    pass
\ No newline at end of file