path: root/Lib/test/test_import/__init__.py

import builtins
import contextlib
import errno
import glob
import importlib.util
from importlib._bootstrap_external import _get_sourcefile
import marshal
import os
import py_compile
import random
import shutil
import stat
import subprocess
import sys
import textwrap
import threading
import time
import unittest
from unittest import mock

from test.support import os_helper
from test.support import (
    STDLIB_DIR, is_jython, swap_attr, swap_item, cpython_only, is_emscripten,
    is_wasi)
from test.support.import_helper import (
    forget, make_legacy_pyc, unlink, unload, DirsOnSysPath, CleanImport)
from test.support.os_helper import (
    TESTFN, rmtree, temp_umask, TESTFN_UNENCODABLE, temp_dir)
from test.support import script_helper
from test.support import threading_helper
from test.test_importlib.util import uncache
from types import ModuleType


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 CleanImport('os'):
            import os
            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')
        if hasattr(_testcapi, "__file__"):
            self.assertEqual(cm.exception.path, _testcapi.__file__)
            self.assertRegex(
                str(cm.exception),
                r"cannot import name 'i_dont_exist' from '_testcapi' \(.*\.(so|pyd)\)"
            )
        else:
            self.assertEqual(
                str(cm.exception),
                "cannot import name 'i_dont_exist' from '_testcapi' (unknown location)"
            )

    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', encoding='utf-8') 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', encoding='utf-8') 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", encoding='utf-8') 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', encoding='utf-8') 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", encoding='utf-8') 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", encoding='utf-8') 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", encoding='utf-8') 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", encoding='utf-8') 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', encoding='utf-8') 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

    @threading_helper.requires_working_threading()
    def test_concurrency(self):
        # bpo 38091: this is a hack to slow down the code that calls
        # has_deadlock(); the logic was itself sometimes deadlocking.
        def delay_has_deadlock(frame, event, arg):
            if event == 'call' and frame.f_code.co_name == 'has_deadlock':
                time.sleep(0.1)

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

            for i in range(10):
                event = threading.Event()
                threads = [threading.Thread(target=run) for x in range(2)]
                try:
                    with threading_helper.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 os_helper.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 + ";" + STDLIB_DIR

            # 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")
    @unittest.skipIf(
        is_emscripten or is_wasi,
        "Emscripten's/WASI's umask is a stub."
    )
    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")
    @os_helper.skip_unless_working_chmod
    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")
    @os_helper.skip_unless_working_chmod
    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', encoding='utf-8') 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', encoding='utf-8') 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", encoding='utf-8') 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', encoding='utf-8') 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', encoding='utf-8') 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")
    @skip_if_dont_write_bytecode
    @os_helper.skip_unless_working_chmod
    @os_helper.skip_if_dac_override
    @unittest.skipIf(is_emscripten, "umask is a stub")
    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.getcwd(), 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.getcwd(), 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.getcwd(), 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'), 'wb'):
            pass
        with open(os.path.join('pep3147', 'foo.py'), 'wb'):
            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.getcwd(), 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.getcwd(), 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'), 'wb'):
            pass
        with open(os.path.join('pep3147', 'foo.py'), 'wb'):
            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.getcwd(), 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.getcwd(), 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', encoding='utf-8') 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):
        os_helper.rmtree(self.tagged)
        os_helper.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(os_helper.rmtree, self.tagged)
        init_file = os.path.join(self.tagged, '__init__.py')
        os_helper.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(os_helper.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")
    @os_helper.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", encoding='utf-8') 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', encoding='utf-8') as f:
            f.write(parent)
        bar_path = os.path.join(pkg_path, 'bar.py')
        with open(bar_path, 'w', encoding='utf-8') 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),
        )

    def test_absolute_circular_submodule(self):
        with self.assertRaises(AttributeError) as cm:
            import test.test_import.data.circular_imports.subpkg2.parent
        self.assertIn(
            "cannot access submodule 'parent' of module "
            "'test.test_import.data.circular_imports.subpkg2' "
            "(most likely due to a circular import)",
            str(cm.exception),
        )

    def test_unwritable_module(self):
        self.addCleanup(unload, "test.test_import.data.unwritable")
        self.addCleanup(unload, "test.test_import.data.unwritable.x")

        import test.test_import.data.unwritable as unwritable
        with self.assertWarns(ImportWarning):
            from test.test_import.data.unwritable import x

        self.assertNotEqual(type(unwritable), ModuleType)
        self.assertEqual(type(x), ModuleType)
        with self.assertRaises(AttributeError):
            unwritable.x = 42


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