diff --git a/Lib/ctypes/test/test_find.py b/Lib/ctypes/test/test_find.py
index 4a8a382..1ff9d01 100644
--- a/Lib/ctypes/test/test_find.py
+++ b/Lib/ctypes/test/test_find.py
@@ -90,7 +90,7 @@ def test_find_on_libpath(self):
             srcname = os.path.join(d, 'dummy.c')
             libname = 'py_ctypes_test_dummy'
             dstname = os.path.join(d, 'lib%s.so' % libname)
-            with open(srcname, 'w') as f:
+            with open(srcname, 'wb') as f:
                 pass
             self.assertTrue(os.path.exists(srcname))
             # compile the file to a shared library
diff --git a/Lib/os.py b/Lib/os.py
index 05e9c32..ea09e8c 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -1020,11 +1020,13 @@ def __iter__(self):
     __all__.append("popen")
 
 # Supply os.fdopen()
-def fdopen(fd, *args, **kwargs):
+def fdopen(fd, mode="r", buffering=-1, encoding=None, *args, **kwargs):
     if not isinstance(fd, int):
         raise TypeError("invalid fd type (%s, expected integer)" % type(fd))
     import io
-    return io.open(fd, *args, **kwargs)
+    if "b" not in mode:
+        encoding = io.text_encoding(encoding)
+    return io.open(fd, mode, buffering, encoding, *args, **kwargs)
 
 
 # For testing purposes, make sure the function is available when the C
diff --git a/Lib/test/_test_multiprocessing.py b/Lib/test/_test_multiprocessing.py
index fd3b430..ead92cf 100644
--- a/Lib/test/_test_multiprocessing.py
+++ b/Lib/test/_test_multiprocessing.py
@@ -826,7 +826,7 @@ def test_stderr_flush(self):
         proc = self.Process(target=self._test_stderr_flush, args=(testfn,))
         proc.start()
         proc.join()
-        with open(testfn, 'r') as f:
+        with open(testfn, encoding="utf-8") as f:
             err = f.read()
             # The whole traceback was printed
             self.assertIn("ZeroDivisionError", err)
@@ -836,14 +836,14 @@ def test_stderr_flush(self):
     @classmethod
     def _test_stderr_flush(cls, testfn):
         fd = os.open(testfn, os.O_WRONLY | os.O_CREAT | os.O_EXCL)
-        sys.stderr = open(fd, 'w', closefd=False)
+        sys.stderr = open(fd, 'w', encoding="utf-8", closefd=False)
         1/0 # MARKER
 
 
     @classmethod
     def _test_sys_exit(cls, reason, testfn):
         fd = os.open(testfn, os.O_WRONLY | os.O_CREAT | os.O_EXCL)
-        sys.stderr = open(fd, 'w', closefd=False)
+        sys.stderr = open(fd, 'w', encoding="utf-8", closefd=False)
         sys.exit(reason)
 
     def test_sys_exit(self):
@@ -864,7 +864,7 @@ def test_sys_exit(self):
             join_process(p)
             self.assertEqual(p.exitcode, 1)
 
-            with open(testfn, 'r') as f:
+            with open(testfn, encoding="utf-8") as f:
                 content = f.read()
             self.assertEqual(content.rstrip(), str(reason))
 
@@ -1118,7 +1118,7 @@ def test_task_done(self):
     def test_no_import_lock_contention(self):
         with os_helper.temp_cwd():
             module_name = 'imported_by_an_imported_module'
-            with open(module_name + '.py', 'w') as f:
+            with open(module_name + '.py', 'w', encoding="utf-8") as f:
                 f.write("""if 1:
                     import multiprocessing
 
diff --git a/Lib/test/multibytecodec_support.py b/Lib/test/multibytecodec_support.py
index f76c015..dbf0cc4 100644
--- a/Lib/test/multibytecodec_support.py
+++ b/Lib/test/multibytecodec_support.py
@@ -296,7 +296,7 @@ def setUp(self):
             self.skipTest("Could not retrieve "+self.mapfileurl)
 
     def open_mapping_file(self):
-        return support.open_urlresource(self.mapfileurl)
+        return support.open_urlresource(self.mapfileurl, encoding="utf-8")
 
     def test_mapping_file(self):
         if self.mapfileurl.endswith('.xml'):
diff --git a/Lib/test/test_asyncio/test_base_events.py b/Lib/test/test_asyncio/test_base_events.py
index e40e799..5691d42 100644
--- a/Lib/test/test_asyncio/test_base_events.py
+++ b/Lib/test/test_asyncio/test_base_events.py
@@ -2096,7 +2096,7 @@ def test_blocking_socket(self):
 
     def test_nonbinary_file(self):
         sock = self.make_socket()
-        with open(os_helper.TESTFN, 'r') as f:
+        with open(os_helper.TESTFN, encoding="utf-8") as f:
             with self.assertRaisesRegex(ValueError, "binary mode"):
                 self.run_loop(self.loop.sock_sendfile(sock, f))
 
diff --git a/Lib/test/test_asyncio/test_events.py b/Lib/test/test_asyncio/test_events.py
index 6523a79..5511407 100644
--- a/Lib/test/test_asyncio/test_events.py
+++ b/Lib/test/test_asyncio/test_events.py
@@ -1349,7 +1349,7 @@ def test_unclosed_pipe_transport(self):
 
         rpipe, wpipe = os.pipe()
         rpipeobj = io.open(rpipe, 'rb', 1024)
-        wpipeobj = io.open(wpipe, 'w', 1024)
+        wpipeobj = io.open(wpipe, 'w', 1024, encoding="utf-8")
 
         async def connect():
             read_transport, _ = await loop.connect_read_pipe(
diff --git a/Lib/test/test_bz2.py b/Lib/test/test_bz2.py
index ccc5e4d..efed3a8 100644
--- a/Lib/test/test_bz2.py
+++ b/Lib/test/test_bz2.py
@@ -922,14 +922,14 @@ def test_text_modes(self):
         for mode in ("wt", "xt"):
             if mode == "xt":
                 unlink(self.filename)
-            with self.open(self.filename, mode) as f:
+            with self.open(self.filename, mode, encoding="ascii") as f:
                 f.write(text)
             with open(self.filename, "rb") as f:
                 file_data = ext_decompress(f.read()).decode("ascii")
                 self.assertEqual(file_data, text_native_eol)
-            with self.open(self.filename, "rt") as f:
+            with self.open(self.filename, "rt", encoding="ascii") as f:
                 self.assertEqual(f.read(), text)
-            with self.open(self.filename, "at") as f:
+            with self.open(self.filename, "at", encoding="ascii") as f:
                 f.write(text)
             with open(self.filename, "rb") as f:
                 file_data = ext_decompress(f.read()).decode("ascii")
@@ -938,7 +938,8 @@ def test_text_modes(self):
     def test_x_mode(self):
         for mode in ("x", "xb", "xt"):
             unlink(self.filename)
-            with self.open(self.filename, mode) as f:
+            encoding = "utf-8" if "t" in mode else None
+            with self.open(self.filename, mode, encoding=encoding) as f:
                 pass
             with self.assertRaises(FileExistsError):
                 with self.open(self.filename, mode) as f:
@@ -950,7 +951,7 @@ def test_fileobj(self):
         with self.open(BytesIO(self.DATA), "rb") as f:
             self.assertEqual(f.read(), self.TEXT)
         text = self.TEXT.decode("ascii")
-        with self.open(BytesIO(self.DATA), "rt") as f:
+        with self.open(BytesIO(self.DATA), "rt", encoding="utf-8") as f:
             self.assertEqual(f.read(), text)
 
     def test_bad_params(self):
@@ -989,9 +990,9 @@ def test_encoding_error_handler(self):
     def test_newline(self):
         # Test with explicit newline (universal newline mode disabled).
         text = self.TEXT.decode("ascii")
-        with self.open(self.filename, "wt", newline="\n") as f:
+        with self.open(self.filename, "wt", encoding="utf-8", newline="\n") as f:
             f.write(text)
-        with self.open(self.filename, "rt", newline="\r") as f:
+        with self.open(self.filename, "rt", encoding="utf-8", newline="\r") as f:
             self.assertEqual(f.readlines(), [text])
 
 
diff --git a/Lib/test/test_cmath.py b/Lib/test/test_cmath.py
index 668f27c..9bb9393 100644
--- a/Lib/test/test_cmath.py
+++ b/Lib/test/test_cmath.py
@@ -60,7 +60,7 @@ class CMathTests(unittest.TestCase):
     test_functions.append(lambda x : cmath.log(14.-27j, x))
 
     def setUp(self):
-        self.test_values = open(test_file)
+        self.test_values = open(test_file, encoding="utf-8")
 
     def tearDown(self):
         self.test_values.close()
diff --git a/Lib/test/test_cmd_line.py b/Lib/test/test_cmd_line.py
index 25d3eec..3758767 100644
--- a/Lib/test/test_cmd_line.py
+++ b/Lib/test/test_cmd_line.py
@@ -512,7 +512,7 @@ def test_del___main__(self):
         # the dict whereas the module was destroyed
         filename = os_helper.TESTFN
         self.addCleanup(os_helper.unlink, filename)
-        with open(filename, "w") as script:
+        with open(filename, "w", encoding="utf-8") as script:
             print("import sys", file=script)
             print("del sys.modules['__main__']", file=script)
         assert_python_ok(filename)
@@ -549,9 +549,9 @@ def test_isolatedmode(self):
         with os_helper.temp_cwd() as tmpdir:
             fake = os.path.join(tmpdir, "uuid.py")
             main = os.path.join(tmpdir, "main.py")
-            with open(fake, "w") as f:
+            with open(fake, "w", encoding="utf-8") as f:
                 f.write("raise RuntimeError('isolated mode test')\n")
-            with open(main, "w") as f:
+            with open(main, "w", encoding="utf-8") as f:
                 f.write("import uuid\n")
                 f.write("print('ok')\n")
             self.assertRaises(subprocess.CalledProcessError,
diff --git a/Lib/test/test_cmd_line_script.py b/Lib/test/test_cmd_line_script.py
index f10ab40..8f12b1e 100644
--- a/Lib/test/test_cmd_line_script.py
+++ b/Lib/test/test_cmd_line_script.py
@@ -400,7 +400,7 @@ def test_issue8202_dash_c_file_ignored(self):
         # does not alter the value of sys.path[0]
         with os_helper.temp_dir() as script_dir:
             with os_helper.change_cwd(path=script_dir):
-                with open("-c", "w") as f:
+                with open("-c", "w", encoding="utf-8") as f:
                     f.write("data")
                     rc, out, err = assert_python_ok('-c',
                         'import sys; print("sys.path[0]==%r" % sys.path[0])',
@@ -416,7 +416,7 @@ def test_issue8202_dash_m_file_ignored(self):
         with os_helper.temp_dir() as script_dir:
             script_name = _make_test_script(script_dir, 'other')
             with os_helper.change_cwd(path=script_dir):
-                with open("-m", "w") as f:
+                with open("-m", "w", encoding="utf-8") as f:
                     f.write("data")
                     rc, out, err = assert_python_ok('-m', 'other', *example_args,
                                                     __isolated=False)
@@ -429,7 +429,7 @@ def test_issue20884(self):
         # will be failed.
         with os_helper.temp_dir() as script_dir:
             script_name = os.path.join(script_dir, "issue20884.py")
-            with open(script_name, "w", newline='\n') as f:
+            with open(script_name, "w", encoding="latin1", newline='\n') as f:
                 f.write("#coding: iso-8859-1\n")
                 f.write('"""\n')
                 for _ in range(30):
diff --git a/Lib/test/test_compile.py b/Lib/test/test_compile.py
index 591d5bb..c0de3be 100644
--- a/Lib/test/test_compile.py
+++ b/Lib/test/test_compile.py
@@ -427,7 +427,7 @@ def test_compile_ast(self):
         fname = __file__
         if fname.lower().endswith('pyc'):
             fname = fname[:-1]
-        with open(fname, 'r') as f:
+        with open(fname, encoding='utf-8') as f:
             fcontents = f.read()
         sample_code = [
             ['<assign>', 'x = 5'],
diff --git a/Lib/test/test_configparser.py b/Lib/test/test_configparser.py
index 80a9f17..9373a62 100644
--- a/Lib/test/test_configparser.py
+++ b/Lib/test/test_configparser.py
@@ -714,31 +714,31 @@ def test_read_returns_file_list(self):
         file1 = support.findfile("cfgparser.1")
         # check when we pass a mix of readable and non-readable files:
         cf = self.newconfig()
-        parsed_files = cf.read([file1, "nonexistent-file"])
+        parsed_files = cf.read([file1, "nonexistent-file"], encoding="utf-8")
         self.assertEqual(parsed_files, [file1])
         self.assertEqual(cf.get("Foo Bar", "foo"), "newbar")
         # check when we pass only a filename:
         cf = self.newconfig()
-        parsed_files = cf.read(file1)
+        parsed_files = cf.read(file1, encoding="utf-8")
         self.assertEqual(parsed_files, [file1])
         self.assertEqual(cf.get("Foo Bar", "foo"), "newbar")
         # check when we pass only a Path object:
         cf = self.newconfig()
-        parsed_files = cf.read(pathlib.Path(file1))
+        parsed_files = cf.read(pathlib.Path(file1), encoding="utf-8")
         self.assertEqual(parsed_files, [file1])
         self.assertEqual(cf.get("Foo Bar", "foo"), "newbar")
         # check when we passed both a filename and a Path object:
         cf = self.newconfig()
-        parsed_files = cf.read([pathlib.Path(file1), file1])
+        parsed_files = cf.read([pathlib.Path(file1), file1], encoding="utf-8")
         self.assertEqual(parsed_files, [file1, file1])
         self.assertEqual(cf.get("Foo Bar", "foo"), "newbar")
         # check when we pass only missing files:
         cf = self.newconfig()
-        parsed_files = cf.read(["nonexistent-file"])
+        parsed_files = cf.read(["nonexistent-file"], encoding="utf-8")
         self.assertEqual(parsed_files, [])
         # check when we pass no files:
         cf = self.newconfig()
-        parsed_files = cf.read([])
+        parsed_files = cf.read([], encoding="utf-8")
         self.assertEqual(parsed_files, [])
 
     def test_read_returns_file_list_with_bytestring_path(self):
@@ -747,15 +747,15 @@ def test_read_returns_file_list_with_bytestring_path(self):
         file1_bytestring = support.findfile("cfgparser.1").encode()
         # check when passing an existing bytestring path
         cf = self.newconfig()
-        parsed_files = cf.read(file1_bytestring)
+        parsed_files = cf.read(file1_bytestring, encoding="utf-8")
         self.assertEqual(parsed_files, [file1_bytestring])
         # check when passing an non-existing bytestring path
         cf = self.newconfig()
-        parsed_files = cf.read(b'nonexistent-file')
+        parsed_files = cf.read(b'nonexistent-file', encoding="utf-8")
         self.assertEqual(parsed_files, [])
         # check when passing both an existing and non-existing bytestring path
         cf = self.newconfig()
-        parsed_files = cf.read([file1_bytestring, b'nonexistent-file'])
+        parsed_files = cf.read([file1_bytestring, b'nonexistent-file'], encoding="utf-8")
         self.assertEqual(parsed_files, [file1_bytestring])
 
     # shared by subclasses
@@ -1064,7 +1064,7 @@ def setUp(self):
             cf.add_section(s)
             for j in range(10):
                 cf.set(s, 'lovely_spam{}'.format(j), self.wonderful_spam)
-        with open(os_helper.TESTFN, 'w') as f:
+        with open(os_helper.TESTFN, 'w', encoding="utf-8") as f:
             cf.write(f)
 
     def tearDown(self):
@@ -1074,7 +1074,7 @@ def test_dominating_multiline_values(self):
         # We're reading from file because this is where the code changed
         # during performance updates in Python 3.2
         cf_from_file = self.newconfig()
-        with open(os_helper.TESTFN) as f:
+        with open(os_helper.TESTFN, encoding="utf-8") as f:
             cf_from_file.read_file(f)
         self.assertEqual(cf_from_file.get('section8', 'lovely_spam4'),
                          self.wonderful_spam.replace('\t\n', '\n'))
@@ -1473,7 +1473,7 @@ def fromstring(self, string, defaults=None):
 class FakeFile:
     def __init__(self):
         file_path = support.findfile("cfgparser.1")
-        with open(file_path) as f:
+        with open(file_path, encoding="utf-8") as f:
             self.lines = f.readlines()
             self.lines.reverse()
 
@@ -1500,7 +1500,7 @@ def test_file(self):
             pass   # unfortunately we can't test bytes on this path
         for file_path in file_paths:
             parser = configparser.ConfigParser()
-            with open(file_path) as f:
+            with open(file_path, encoding="utf-8") as f:
                 parser.read_file(f)
             self.assertIn("Foo Bar", parser)
             self.assertIn("foo", parser["Foo Bar"])
diff --git a/Lib/test/test_contextlib.py b/Lib/test/test_contextlib.py
index 50943c1..453ef6c 100644
--- a/Lib/test/test_contextlib.py
+++ b/Lib/test/test_contextlib.py
@@ -316,13 +316,13 @@ def testWithOpen(self):
         tfn = tempfile.mktemp()
         try:
             f = None
-            with open(tfn, "w") as f:
+            with open(tfn, "w", encoding="utf-8") as f:
                 self.assertFalse(f.closed)
                 f.write("Booh\n")
             self.assertTrue(f.closed)
             f = None
             with self.assertRaises(ZeroDivisionError):
-                with open(tfn, "r") as f:
+                with open(tfn, "r", encoding="utf-8") as f:
                     self.assertFalse(f.closed)
                     self.assertEqual(f.read(), "Booh\n")
                     1 / 0
diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
index a98707c..2411a91 100644
--- a/Lib/test/test_csv.py
+++ b/Lib/test/test_csv.py
@@ -133,7 +133,7 @@ def test_writer_dialect_attrs(self):
 
 
     def _write_test(self, fields, expect, **kwargs):
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj, **kwargs)
             writer.writerow(fields)
             fileobj.seek(0)
@@ -141,7 +141,7 @@ def _write_test(self, fields, expect, **kwargs):
                              expect + writer.dialect.lineterminator)
 
     def _write_error_test(self, exc, fields, **kwargs):
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj, **kwargs)
             with self.assertRaises(exc):
                 writer.writerow(fields)
@@ -232,7 +232,7 @@ def write(self, buf):
         writer = csv.writer(BrokenFile())
         self.assertRaises(OSError, writer.writerows, [['a']])
 
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj)
             self.assertRaises(TypeError, writer.writerows, None)
             writer.writerows([['a', 'b'], ['c', 'd']])
@@ -240,26 +240,26 @@ def write(self, buf):
             self.assertEqual(fileobj.read(), "a,b\r\nc,d\r\n")
 
     def test_writerows_with_none(self):
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj)
             writer.writerows([['a', None], [None, 'd']])
             fileobj.seek(0)
             self.assertEqual(fileobj.read(), "a,\r\n,d\r\n")
 
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj)
             writer.writerows([[None], ['a']])
             fileobj.seek(0)
             self.assertEqual(fileobj.read(), '""\r\na\r\n')
 
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj)
             writer.writerows([['a'], [None]])
             fileobj.seek(0)
             self.assertEqual(fileobj.read(), 'a\r\n""\r\n')
 
     def test_writerows_errors(self):
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj)
             self.assertRaises(TypeError, writer.writerows, None)
             self.assertRaises(OSError, writer.writerows, BadIterable())
@@ -270,7 +270,7 @@ def test_writerows_errors(self):
     def test_writerows_legacy_strings(self):
         import _testcapi
         c = _testcapi.unicode_legacy_string('a')
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj)
             writer.writerows([[c]])
             fileobj.seek(0)
@@ -367,7 +367,7 @@ def test_read_linenum(self):
         self.assertEqual(r.line_num, 3)
 
     def test_roundtrip_quoteed_newlines(self):
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj)
             rows = [['a\nb','b'],['c','x\r\nd']]
             writer.writerows(rows)
@@ -376,7 +376,7 @@ def test_roundtrip_quoteed_newlines(self):
                 self.assertEqual(row, rows[i])
 
     def test_roundtrip_escaped_unquoted_newlines(self):
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj,quoting=csv.QUOTE_NONE,escapechar="\\")
             rows = [['a\nb','b'],['c','x\r\nd']]
             writer.writerows(rows)
@@ -432,7 +432,7 @@ class space(csv.excel):
             quoting = csv.QUOTE_NONE
             escapechar = "\\"
 
-        with TemporaryFile("w+") as fileobj:
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
             fileobj.write("abc def\nc1ccccc1 benzene\n")
             fileobj.seek(0)
             reader = csv.reader(fileobj, dialect=space())
@@ -493,7 +493,7 @@ def test_pickle(self):
 
 class TestCsvBase(unittest.TestCase):
     def readerAssertEqual(self, input, expected_result):
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             fileobj.write(input)
             fileobj.seek(0)
             reader = csv.reader(fileobj, dialect = self.dialect)
@@ -501,7 +501,7 @@ def readerAssertEqual(self, input, expected_result):
             self.assertEqual(fields, expected_result)
 
     def writerAssertEqual(self, input, expected_result):
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj, dialect = self.dialect)
             writer.writerows(input)
             fileobj.seek(0)
@@ -643,13 +643,13 @@ class TestDictFields(unittest.TestCase):
     ### "long" means the row is longer than the number of fieldnames
     ### "short" means there are fewer elements in the row than fieldnames
     def test_writeheader_return_value(self):
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.DictWriter(fileobj, fieldnames = ["f1", "f2", "f3"])
             writeheader_return_value = writer.writeheader()
             self.assertEqual(writeheader_return_value, 10)
 
     def test_write_simple_dict(self):
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.DictWriter(fileobj, fieldnames = ["f1", "f2", "f3"])
             writer.writeheader()
             fileobj.seek(0)
@@ -674,7 +674,7 @@ def test_write_no_fields(self):
         self.assertRaises(TypeError, csv.DictWriter, fileobj)
 
     def test_write_fields_not_in_fieldnames(self):
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.DictWriter(fileobj, fieldnames = ["f1", "f2", "f3"])
             # Of special note is the non-string key (issue 19449)
             with self.assertRaises(ValueError) as cx:
@@ -704,7 +704,7 @@ def test_write_field_not_in_field_names_ignore(self):
         self.assertEqual(fileobj.getvalue(), "1,2\r\n")
 
     def test_read_dict_fields(self):
-        with TemporaryFile("w+") as fileobj:
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
             fileobj.write("1,2,abc\r\n")
             fileobj.seek(0)
             reader = csv.DictReader(fileobj,
@@ -712,7 +712,7 @@ def test_read_dict_fields(self):
             self.assertEqual(next(reader), {"f1": '1', "f2": '2', "f3": 'abc'})
 
     def test_read_dict_no_fieldnames(self):
-        with TemporaryFile("w+") as fileobj:
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
             fileobj.write("f1,f2,f3\r\n1,2,abc\r\n")
             fileobj.seek(0)
             reader = csv.DictReader(fileobj)
@@ -722,7 +722,7 @@ def test_read_dict_no_fieldnames(self):
     # Two test cases to make sure existing ways of implicitly setting
     # fieldnames continue to work.  Both arise from discussion in issue3436.
     def test_read_dict_fieldnames_from_file(self):
-        with TemporaryFile("w+") as fileobj:
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
             fileobj.write("f1,f2,f3\r\n1,2,abc\r\n")
             fileobj.seek(0)
             reader = csv.DictReader(fileobj,
@@ -732,7 +732,7 @@ def test_read_dict_fieldnames_from_file(self):
 
     def test_read_dict_fieldnames_chain(self):
         import itertools
-        with TemporaryFile("w+") as fileobj:
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
             fileobj.write("f1,f2,f3\r\n1,2,abc\r\n")
             fileobj.seek(0)
             reader = csv.DictReader(fileobj)
@@ -742,7 +742,7 @@ def test_read_dict_fieldnames_chain(self):
                 self.assertEqual(row, {"f1": '1', "f2": '2', "f3": 'abc'})
 
     def test_read_long(self):
-        with TemporaryFile("w+") as fileobj:
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
             fileobj.write("1,2,abc,4,5,6\r\n")
             fileobj.seek(0)
             reader = csv.DictReader(fileobj,
@@ -751,7 +751,7 @@ def test_read_long(self):
                                              None: ["abc", "4", "5", "6"]})
 
     def test_read_long_with_rest(self):
-        with TemporaryFile("w+") as fileobj:
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
             fileobj.write("1,2,abc,4,5,6\r\n")
             fileobj.seek(0)
             reader = csv.DictReader(fileobj,
@@ -760,7 +760,7 @@ def test_read_long_with_rest(self):
                                              "_rest": ["abc", "4", "5", "6"]})
 
     def test_read_long_with_rest_no_fieldnames(self):
-        with TemporaryFile("w+") as fileobj:
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
             fileobj.write("f1,f2\r\n1,2,abc,4,5,6\r\n")
             fileobj.seek(0)
             reader = csv.DictReader(fileobj, restkey="_rest")
@@ -769,7 +769,7 @@ def test_read_long_with_rest_no_fieldnames(self):
                                              "_rest": ["abc", "4", "5", "6"]})
 
     def test_read_short(self):
-        with TemporaryFile("w+") as fileobj:
+        with TemporaryFile("w+", encoding="utf-8") as fileobj:
             fileobj.write("1,2,abc,4,5,6\r\n1,2,abc\r\n")
             fileobj.seek(0)
             reader = csv.DictReader(fileobj,
@@ -818,7 +818,7 @@ def test_int_write(self):
         contents = [(20-i) for i in range(20)]
         a = array.array('i', contents)
 
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj, dialect="excel")
             writer.writerow(a)
             expected = ",".join([str(i) for i in a])+"\r\n"
@@ -829,7 +829,7 @@ def test_double_write(self):
         import array
         contents = [(20-i)*0.1 for i in range(20)]
         a = array.array('d', contents)
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj, dialect="excel")
             writer.writerow(a)
             expected = ",".join([str(i) for i in a])+"\r\n"
@@ -840,7 +840,7 @@ def test_float_write(self):
         import array
         contents = [(20-i)*0.1 for i in range(20)]
         a = array.array('f', contents)
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj, dialect="excel")
             writer.writerow(a)
             expected = ",".join([str(i) for i in a])+"\r\n"
@@ -851,7 +851,7 @@ def test_char_write(self):
         import array, string
         a = array.array('u', string.ascii_letters)
 
-        with TemporaryFile("w+", newline='') as fileobj:
+        with TemporaryFile("w+", encoding="utf-8", newline='') as fileobj:
             writer = csv.writer(fileobj, dialect="excel")
             writer.writerow(a)
             expected = ",".join(a)+"\r\n"
diff --git a/Lib/test/test_dbm_dumb.py b/Lib/test/test_dbm_dumb.py
index 071cb84..ddaffb4 100644
--- a/Lib/test/test_dbm_dumb.py
+++ b/Lib/test/test_dbm_dumb.py
@@ -232,7 +232,7 @@ def test_create_new(self):
             self.assertEqual(f.keys(), [])
 
     def test_eval(self):
-        with open(_fname + '.dir', 'w') as stream:
+        with open(_fname + '.dir', 'w', encoding="utf-8") as stream:
             stream.write("str(print('Hacked!')), 0\n")
         with support.captured_stdout() as stdout:
             with self.assertRaises(ValueError):
diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
index 6aa4a9b..179a9ea 100644
--- a/Lib/test/test_decimal.py
+++ b/Lib/test/test_decimal.py
@@ -289,7 +289,7 @@ def eval_file(self, file):
         global skip_expected
         if skip_expected:
             raise unittest.SkipTest
-        with open(file) as f:
+        with open(file, encoding="utf-8") as f:
             for line in f:
                 line = line.replace('\r\n', '').replace('\n', '')
                 #print line
diff --git a/Lib/test/test_difflib.py b/Lib/test/test_difflib.py
index 42ac1fd..9a24e00 100644
--- a/Lib/test/test_difflib.py
+++ b/Lib/test/test_difflib.py
@@ -241,7 +241,7 @@ def test_html_diff(self):
         #with open('test_difflib_expect.html','w') as fp:
         #    fp.write(actual)
 
-        with open(findfile('test_difflib_expect.html')) as fp:
+        with open(findfile('test_difflib_expect.html'), encoding="utf-8") as fp:
             self.assertEqual(actual, fp.read())
 
     def test_recursion_limit(self):
diff --git a/Lib/test/test_math.py b/Lib/test/test_math.py
index a6f6483..3d12874 100644
--- a/Lib/test/test_math.py
+++ b/Lib/test/test_math.py
@@ -130,7 +130,7 @@ def parse_mtestfile(fname):
       id fn arg -> expected [flag]*
 
     """
-    with open(fname) as fp:
+    with open(fname, encoding="utf-8") as fp:
         for line in fp:
             # strip comments, and skip blank lines
             if '--' in line:
@@ -153,7 +153,7 @@ def parse_testfile(fname):
     Empty lines or lines starting with -- are ignored
     yields id, fn, arg_real, arg_imag, exp_real, exp_imag
     """
-    with open(fname) as fp:
+    with open(fname, encoding="utf-8") as fp:
         for line in fp:
             # skip comment lines and blank lines
             if line.startswith('--') or not line.strip():
diff --git a/Lib/test/test_profile.py b/Lib/test/test_profile.py
index 1bdf30a..7de7d52 100644
--- a/Lib/test/test_profile.py
+++ b/Lib/test/test_profile.py
@@ -115,7 +115,7 @@ def test_run_profile_as_module(self):
     def test_output_file_when_changing_directory(self):
         with temp_dir() as tmpdir, change_cwd(tmpdir):
             os.mkdir('dest')
-            with open('demo.py', 'w') as f:
+            with open('demo.py', 'w', encoding="utf-8") as f:
                 f.write('import os; os.chdir("dest")')
 
             assert_python_ok(