test/test_import/__init__.py

# We import importlib *ASAP* in order to test #15386
import importlib
import importlib.util
from importlib._bootstrap_external import _get_sourcefile
import builtins
import marshal
import os
import py_compile
import random
import shutil
import subprocess
import stat
import sys
import threading
import time
import unittest
import unittest.mock as mock
import textwrap
import errno
import contextlib
import glob

import test.support
from test.support import (
    TESTFN, forget, is_jython,
    make_legacy_pyc, rmtree, swap_attr, swap_item, temp_umask,
    unlink, unload, cpython_only, TESTFN_UNENCODABLE,
    temp_dir, DirsOnSysPath)
from test.support import script_helper
from test.test_importlib.util import uncache


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 + ".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 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_import_raises_ModuleNotFoundError(self):
        with self.assertRaises(ModuleNotFoundError):
            import something_that_should_not_exist_anywhere

    def test_from_import_missing_module_raises_ModuleNotFoundError(self):
        with self.assertRaises(ModuleNotFoundError):
            from something_that_should_not_exist_anywhere import blah

    def test_from_import_missing_attr_raises_ImportError(self):
        with self.assertRaises(ImportError):
            from importlib import something_that_should_not_exist_anywhere

    def test_from_import_missing_attr_has_name_and_path(self):
        with self.assertRaises(ImportError) as cm:
            from os import i_dont_exist
        self.assertEqual(cm.exception.name, 'os')
        self.assertEqual(cm.exception.path, os.__file__)
        self.assertRegex(str(cm.exception), r"cannot import name 'i_dont_exist' from 'os' \(.*os.py\)")

    @cpython_only
    def test_from_import_missing_attr_has_name_and_so_path(self):
        import _testcapi
        with self.assertRaises(ImportError) as cm:
            from _testcapi import i_dont_exist
        self.assertEqual(cm.exception.name, '_testcapi')
        self.assertEqual(cm.exception.path, _testcapi.__file__)
        self.assertRegex(str(cm.exception), r"cannot import name 'i_dont_exist' from '_testcapi' \(.*\.(so|pyd)\)")

    def test_from_import_missing_attr_has_name(self):
        with self.assertRaises(ImportError) as cm:
            # _warning has no path as it's a built-in module.
            from _warning import i_dont_exist
        self.assertEqual(cm.exception.name, '_warning')
        self.assertIsNone(cm.exception.path)

    def test_from_import_missing_attr_path_is_canonical(self):
        with self.assertRaises(ImportError) as cm:
            from os.path import i_dont_exist
        self.assertIn(cm.exception.name, {'posixpath', 'ntpath'})
        self.assertIsNotNone(cm.exception)

    def test_from_import_star_invalid_type(self):
        import re
        with _ready_to_import() as (name, path):
            with open(path, 'w') as f:
                f.write("__all__ = [b'invalid_type']")
            globals = {}
            with self.assertRaisesRegex(
                TypeError, f"{re.escape(name)}\\.__all__ must be str"
            ):
                exec(f"from {name} import *", globals)
            self.assertNotIn(b"invalid_type", globals)
        with _ready_to_import() as (name, path):
            with open(path, 'w') as f:
                f.write("globals()[b'invalid_type'] = object()")
            globals = {}
            with self.assertRaisesRegex(
                TypeError, f"{re.escape(name)}\\.__dict__ must be str"
            ):
                exec(f"from {name} import *", globals)
            self.assertNotIn(b"invalid_type", globals)

    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
            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)

        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.
            # 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_issue31286(self):
        # import in a 'finally' block resulted in SystemError
        try:
            x = ...
        finally:
            import test.support.script_helper as x

        # import in a 'while' loop resulted in stack overflow
        i = 0
        while i < 10:
            import test.support.script_helper as x
            i += 1

        # import in a 'for' loop resulted in segmentation fault
        for i in range(2):
            import test.support.script_helper as x

    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.assertEqual(ext, '.pyc')
        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)

    @skip_if_dont_write_bytecode
    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 not in (getattr(errno, 'EOVERFLOW', None),
                                   getattr(errno, 'EINVAL', 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

    def test_from_import_AttributeError(self):
        # Issue #24492: trying to import an attribute that raises an
        # AttributeError should lead to an ImportError.
        class AlwaysAttributeError:
            def __getattr__(self, _):
                raise AttributeError

        module_name = 'test_from_import_AttributeError'
        self.addCleanup(unload, module_name)
        sys.modules[module_name] = AlwaysAttributeError()
        with self.assertRaises(ImportError) as cm:
            from test_from_import_AttributeError import does_not_exist

        self.assertEqual(str(cm.exception),
            "cannot import name 'does_not_exist' from '<unknown module name>' (unknown location)")

    @cpython_only
    def test_issue31492(self):
        # There shouldn't be an assertion failure in case of failing to import
        # from a module with a bad __name__ attribute, or in case of failing
        # to access an attribute of such a module.
        with swap_attr(os, '__name__', None):
            with self.assertRaises(ImportError):
                from os import does_not_exist

            with self.assertRaises(AttributeError):
                os.does_not_exist

    def test_concurrency(self):
        sys.path.insert(0, os.path.join(os.path.dirname(__file__), 'data'))
        try:
            exc = None
            def run():
                event.wait()
                try:
                    import package
                except BaseException as e:
                    nonlocal exc
                    exc = e

            for i in range(10):
                event = threading.Event()
                threads = [threading.Thread(target=run) for x in range(2)]
                try:
                    with test.support.start_threads(threads, event.set):
                        time.sleep(0)
                finally:
                    sys.modules.pop('package', None)
                    sys.modules.pop('package.submodule', None)
                if exc is not None:
                    raise exc
        finally:
            del sys.path[0]

    @unittest.skipUnless(sys.platform == "win32", "Windows-specific")
    def test_dll_dependency_import(self):
        from _winapi import GetModuleFileName
        dllname = GetModuleFileName(sys.dllhandle)
        pydname = importlib.util.find_spec("_sqlite3").origin
        depname = os.path.join(
            os.path.dirname(pydname),
            "sqlite3{}.dll".format("_d" if "_d" in pydname else ""))

        with test.support.temp_dir() as tmp:
            tmp2 = os.path.join(tmp, "DLLs")
            os.mkdir(tmp2)

            pyexe = os.path.join(tmp, os.path.basename(sys.executable))
            shutil.copy(sys.executable, pyexe)
            shutil.copy(dllname, tmp)
            for f in glob.glob(os.path.join(glob.escape(sys.prefix), "vcruntime*.dll")):
                shutil.copy(f, tmp)

            shutil.copy(pydname, tmp2)

            env = None
            env = {k.upper(): os.environ[k] for k in os.environ}
            env["PYTHONPATH"] = tmp2 + ";" + os.path.dirname(os.__file__)

            # Test 1: import with added DLL directory
            subprocess.check_call([
                pyexe, "-Sc", ";".join([
                    "import os",
                    "p = os.add_dll_directory({!r})".format(
                        os.path.dirname(depname)),
                    "import _sqlite3",
                    "p.close"
                ])],
                stderr=subprocess.STDOUT,
                env=env,
                cwd=os.path.dirname(pyexe))

            # Test 2: import with DLL adjacent to PYD
            shutil.copy(depname, tmp2)
            subprocess.check_call([pyexe, "-Sc", "import _sqlite3"],
                                    stderr=subprocess.STDOUT,
                                    env=env,
                                    cwd=os.path.dirname(pyexe))


@skip_if_dont_write_bytecode
class FilePermissionTests(unittest.TestCase):
    # tests for file mode on cached .pyc 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 "
                          "a .pyc 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 "
                          "a .pyc 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 "
                          "a .pyc 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()
            bytecode_only = path + "c"
            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(16)
            code = marshal.load(f)
        constants = list(code.co_consts)
        foreign_code = importlib.import_module.__code__
        pos = constants.index(1)
        constants[pos] = foreign_code
        code = code.replace(co_consts=tuple(constants))
        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, errno.ENOENT):
                # 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(ModuleNotFoundError, check_relative)

        # Check relative import fails with __package__ and __name__ wrong
        ns = dict(__package__='foo', __name__='notarealpkg.notarealmodule')
        self.assertRaises(ModuleNotFoundError, check_relative)

        # Check relative import fails with package set to a non-string
        ns = dict(__package__=object())
        self.assertRaises(TypeError, check_relative)

    def test_parentless_import_shadowed_by_global(self):
        # Test as if this were done from the REPL where this error most commonly occurs (bpo-37409).
        script_helper.assert_python_failure('-W', 'ignore', '-c',
            "foo = 1; from . import foo")

    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")

    def test_import_from_non_package(self):
        path = os.path.join(os.path.dirname(__file__), 'data', 'package2')
        with uncache('submodule1', 'submodule2'), DirsOnSysPath(path):
            with self.assertRaises(ImportError):
                import submodule1
            self.assertNotIn('submodule1', sys.modules)
            self.assertNotIn('submodule2', sys.modules)

    def test_import_from_unloaded_package(self):
        with uncache('package2', 'package2.submodule1', 'package2.submodule2'), \
             DirsOnSysPath(os.path.join(os.path.dirname(__file__), 'data')):
            import package2.submodule1
            package2.submodule1.submodule2


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 3147/488-related behaviors.

    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__'))
        pyc_path = importlib.util.cache_from_source(self.source)
        self.assertTrue(os.path.exists(pyc_path),
                        'bytecode file {!r} for {!r} does not '
                        'exist'.format(pyc_path, TESTFN))

    @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__'))
        pyc_path = importlib.util.cache_from_source(self.source)
        self.assertFalse(os.path.exists(pyc_path),
                        'bytecode file {!r} for {!r} '
                        'exists'.format(pyc_path, TESTFN))

    @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)
        try:
            self.assertEqual(m.__file__,
                             os.path.join(os.curdir, os.path.relpath(pyc_file)))
        finally:
            os.remove(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_frozen_importlib_external_is_bootstrap_external(self):
        from importlib import _bootstrap_external
        mod = sys.modules['_frozen_importlib_external']
        self.assertIs(mod, _bootstrap_external)
        self.assertEqual(mod.__name__, 'importlib._bootstrap_external')
        self.assertEqual(mod.__package__, 'importlib')
        self.assertTrue(mod.__file__.endswith('_bootstrap_external.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.ModuleSpec, mod.ModuleSpec)


@cpython_only
class GetSourcefileTests(unittest.TestCase):

    """Test importlib._bootstrap_external._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_external._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_external._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_external']
        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)

    def test_binding(self):
        try:
            import test.test_import.data.circular_imports.binding
        except ImportError:
            self.fail('circular import with binding a submodule to a name failed')

    def test_crossreference1(self):
        import test.test_import.data.circular_imports.use
        import test.test_import.data.circular_imports.source

    def test_crossreference2(self):
        with self.assertRaises(AttributeError) as cm:
            import test.test_import.data.circular_imports.source
        errmsg = str(cm.exception)
        self.assertIn('test.test_import.data.circular_imports.source', errmsg)
        self.assertIn('spam', errmsg)
        self.assertIn('partially initialized module', errmsg)
        self.assertIn('circular import', errmsg)

    def test_circular_from_import(self):
        with self.assertRaises(ImportError) as cm:
            import test.test_import.data.circular_imports.from_cycle1
        self.assertIn(
            "cannot import name 'b' from partially initialized module "
            "'test.test_import.data.circular_imports.from_cycle1' "
            "(most likely due to a circular import)",
            str(cm.exception),
        )


if __name__ == '__main__':
    # Test needs to be a package, so we can do relative imports.
    unittest.main()