bpo-36346: Make using the legacy Unicode C API optional (GH-21437)

Add compile time option USE_UNICODE_WCHAR_CACHE. Setting it to 0
makes the interpreter not using the wchar_t cache and the legacy Unicode C API.

17 files changed, 360 insertions, 99 deletions

diff --git a/Include/cpython/unicodeobject.h b/Include/cpython/unicodeobject.h
index 49ad32d5d19..615b4a971d5 100644
--- a/Include/cpython/unicodeobject.h
+++ b/Include/cpython/unicodeobject.h
@@ -11,7 +11,9 @@
 
 /* --- Internal Unicode Operations ---------------------------------------- */
 
-#define USE_UNICODE_WCHAR_CACHE 1
+#ifndef USE_UNICODE_WCHAR_CACHE
+#  define USE_UNICODE_WCHAR_CACHE 1
+#endif /* USE_UNICODE_WCHAR_CACHE */
 
 /* Since splitting on whitespace is an important use case, and
    whitespace in most situations is solely ASCII whitespace, we
diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
index b21978a61cd..1ce3a78fdbb 100644
--- a/Lib/test/support/__init__.py
+++ b/Lib/test/support/__init__.py
@@ -36,6 +36,11 @@ from .warnings_helper import (
 from .testresult import get_test_runner
 
 
+try:
+    from _testcapi import unicode_legacy_string
+except ImportError:
+    unicode_legacy_string = None
+
 __all__ = [
     # globals
     "PIPE_MAX_SIZE", "verbose", "max_memuse", "use_resources", "failfast",
@@ -426,6 +431,9 @@ def requires_lzma(reason='requires lzma'):
         lzma = None
     return unittest.skipUnless(lzma, reason)
 
+requires_legacy_unicode_capi = unittest.skipUnless(unicode_legacy_string,
+                        'requires legacy Unicode C API')
+
 is_jython = sys.platform.startswith('java')
 
 is_android = hasattr(sys, 'getandroidapilevel')
diff --git a/Lib/test/test_csv.py b/Lib/test/test_csv.py
index d421be075ca..a92870c24a1 100644
--- a/Lib/test/test_csv.py
+++ b/Lib/test/test_csv.py
@@ -250,9 +250,9 @@ class Test_Csv(unittest.TestCase):
             self.assertRaises(OSError, writer.writerows, BadIterable())
 
     @support.cpython_only
+    @support.requires_legacy_unicode_capi
     def test_writerows_legacy_strings(self):
         import _testcapi
-
         c = _testcapi.unicode_legacy_string('a')
         with TemporaryFile("w+", newline='') as fileobj:
             writer = csv.writer(fileobj)
diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
index 716e6eb7fb1..9dbae449fb6 100644
--- a/Lib/test/test_decimal.py
+++ b/Lib/test/test_decimal.py
@@ -33,7 +33,8 @@ import unittest
 import numbers
 import locale
 from test.support import (run_unittest, run_doctest, is_resource_enabled,
-                          requires_IEEE_754, requires_docstrings)
+                          requires_IEEE_754, requires_docstrings,
+                          requires_legacy_unicode_capi)
 from test.support import (TestFailed,
                           run_with_locale, cpython_only)
 from test.support.import_helper import import_fresh_module
@@ -582,6 +583,7 @@ class ExplicitConstructionTest(unittest.TestCase):
             self.assertRaises(InvalidOperation, Decimal, "1_2_\u00003")
 
     @cpython_only
+    @requires_legacy_unicode_capi
     def test_from_legacy_strings(self):
         import _testcapi
         Decimal = self.decimal.Decimal
@@ -2817,6 +2819,7 @@ class ContextAPItests(unittest.TestCase):
                                               Overflow])
 
     @cpython_only
+    @requires_legacy_unicode_capi
     def test_from_legacy_strings(self):
         import _testcapi
         c = self.decimal.Context()
diff --git a/Lib/test/test_getargs2.py b/Lib/test/test_getargs2.py
index d39ea56ae9e..09560197913 100644
--- a/Lib/test/test_getargs2.py
+++ b/Lib/test/test_getargs2.py
@@ -976,6 +976,7 @@ class String_TestCase(unittest.TestCase):
         buf = bytearray()
         self.assertRaises(ValueError, getargs_et_hash, 'abc\xe9', 'latin1', buf)
 
+    @support.requires_legacy_unicode_capi
     def test_u(self):
         from _testcapi import getargs_u
         self.assertEqual(getargs_u('abc\xe9'), 'abc\xe9')
@@ -985,6 +986,7 @@ class String_TestCase(unittest.TestCase):
         self.assertRaises(TypeError, getargs_u, memoryview(b'memoryview'))
         self.assertRaises(TypeError, getargs_u, None)
 
+    @support.requires_legacy_unicode_capi
     def test_u_hash(self):
         from _testcapi import getargs_u_hash
         self.assertEqual(getargs_u_hash('abc\xe9'), 'abc\xe9')
@@ -994,6 +996,7 @@ class String_TestCase(unittest.TestCase):
         self.assertRaises(TypeError, getargs_u_hash, memoryview(b'memoryview'))
         self.assertRaises(TypeError, getargs_u_hash, None)
 
+    @support.requires_legacy_unicode_capi
     def test_Z(self):
         from _testcapi import getargs_Z
         self.assertEqual(getargs_Z('abc\xe9'), 'abc\xe9')
@@ -1003,6 +1006,7 @@ class String_TestCase(unittest.TestCase):
         self.assertRaises(TypeError, getargs_Z, memoryview(b'memoryview'))
         self.assertIsNone(getargs_Z(None))
 
+    @support.requires_legacy_unicode_capi
     def test_Z_hash(self):
         from _testcapi import getargs_Z_hash
         self.assertEqual(getargs_Z_hash('abc\xe9'), 'abc\xe9')
diff --git a/Lib/test/test_unicode.py b/Lib/test/test_unicode.py
index afc95555db0..d485bc7ede2 100644
--- a/Lib/test/test_unicode.py
+++ b/Lib/test/test_unicode.py
@@ -723,6 +723,7 @@ class UnicodeTest(string_tests.CommonTest,
         self.assertFalse("0".isidentifier())
 
     @support.cpython_only
+    @support.requires_legacy_unicode_capi
     def test_isidentifier_legacy(self):
         import _testcapi
         u = '𝖀𝖓𝖎𝖈𝖔𝖉𝖊'
@@ -2350,6 +2351,7 @@ class UnicodeTest(string_tests.CommonTest,
         self.assertEqual(len(args), 1)
 
     @support.cpython_only
+    @support.requires_legacy_unicode_capi
     def test_resize(self):
         from _testcapi import getargs_u
         for length in range(1, 100, 7):
@@ -2920,6 +2922,7 @@ class CAPITest(unittest.TestCase):
         self.assertRaises(SystemError, unicode_copycharacters, s, 0, b'', 0, 0)
 
     @support.cpython_only
+    @support.requires_legacy_unicode_capi
     def test_encode_decimal(self):
         from _testcapi import unicode_encodedecimal
         self.assertEqual(unicode_encodedecimal('123'),
@@ -2936,6 +2939,7 @@ class CAPITest(unittest.TestCase):
             unicode_encodedecimal, "123\u20ac", "replace")
 
     @support.cpython_only
+    @support.requires_legacy_unicode_capi
     def test_transform_decimal(self):
         from _testcapi import unicode_transformdecimaltoascii as transform_decimal
         self.assertEqual(transform_decimal('123'),
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index 7c8ba37c4fe..b9856b3b631 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -270,7 +270,14 @@ _io_FileIO___init___impl(fileio *self, PyObject *nameobj, const char *mode,
         if (!PyUnicode_FSDecoder(nameobj, &stringobj)) {
             return -1;
         }
+#if USE_UNICODE_WCHAR_CACHE
+_Py_COMP_DIAG_PUSH
+_Py_COMP_DIAG_IGNORE_DEPR_DECLS
         widename = PyUnicode_AsUnicode(stringobj);
+_Py_COMP_DIAG_POP
+#else /* USE_UNICODE_WCHAR_CACHE */
+        widename = PyUnicode_AsWideCharString(stringobj, NULL);
+#endif /* USE_UNICODE_WCHAR_CACHE */
         if (widename == NULL)
             return -1;
 #else
@@ -491,6 +498,11 @@ _io_FileIO___init___impl(fileio *self, PyObject *nameobj, const char *mode,
         internal_close(self);
 
  done:
+#ifdef MS_WINDOWS
+#if !USE_UNICODE_WCHAR_CACHE
+    PyMem_Free(widename);
+#endif /* USE_UNICODE_WCHAR_CACHE */
+#endif
     Py_CLEAR(stringobj);
     return ret;
 }
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index 1e4c31fefb2..fca94a83a5d 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -1668,6 +1668,7 @@ exit:
 
 static volatile int x;
 
+#if USE_UNICODE_WCHAR_CACHE
 /* Ignore use of deprecated APIs */
 _Py_COMP_DIAG_PUSH
 _Py_COMP_DIAG_IGNORE_DEPR_DECLS
@@ -1772,6 +1773,8 @@ test_Z_code(PyObject *self, PyObject *Py_UNUSED(ignored))
     Py_DECREF(tuple);
     Py_RETURN_NONE;
 }
+_Py_COMP_DIAG_POP
+#endif /* USE_UNICODE_WCHAR_CACHE */
 
 static PyObject *
 test_widechar(PyObject *self, PyObject *Py_UNUSED(ignored))
@@ -1824,6 +1827,10 @@ test_widechar(PyObject *self, PyObject *Py_UNUSED(ignored))
         return raiseTestError("test_widechar",
                               "PyUnicode_FromWideChar(L\"\\U00110000\", 1) didn't fail");
 
+#if USE_UNICODE_WCHAR_CACHE
+/* Ignore use of deprecated APIs */
+_Py_COMP_DIAG_PUSH
+_Py_COMP_DIAG_IGNORE_DEPR_DECLS
     wide = PyUnicode_FromUnicode(invalid, 1);
     if (wide == NULL)
         PyErr_Clear();
@@ -1844,11 +1851,12 @@ test_widechar(PyObject *self, PyObject *Py_UNUSED(ignored))
         return raiseTestError("test_widechar",
                               "PyUnicode_Ready() didn't fail");
     }
+_Py_COMP_DIAG_POP
+#endif /* USE_UNICODE_WCHAR_CACHE */
 #endif
 
     Py_RETURN_NONE;
 }
-_Py_COMP_DIAG_POP
 
 static PyObject *
 unicode_aswidechar(PyObject *self, PyObject *args)
@@ -2024,6 +2032,7 @@ unicode_copycharacters(PyObject *self, PyObject *args)
     return Py_BuildValue("(Nn)", to_copy, copied);
 }
 
+#if USE_UNICODE_WCHAR_CACHE
 /* Ignore use of deprecated APIs */
 _Py_COMP_DIAG_PUSH
 _Py_COMP_DIAG_IGNORE_DEPR_DECLS
@@ -2096,6 +2105,7 @@ unicode_legacy_string(PyObject *self, PyObject *args)
     return u;
 }
 _Py_COMP_DIAG_POP
+#endif /* USE_UNICODE_WCHAR_CACHE */
 
 static PyObject *
 getargs_w_star(PyObject *self, PyObject *args)
@@ -5398,8 +5408,10 @@ static PyMethodDef TestMethods[] = {
     {"codec_incrementaldecoder",
      (PyCFunction)codec_incrementaldecoder,                      METH_VARARGS},
     {"test_s_code",             test_s_code,                     METH_NOARGS},
+#if USE_UNICODE_WCHAR_CACHE
     {"test_u_code",             test_u_code,                     METH_NOARGS},
     {"test_Z_code",             test_Z_code,                     METH_NOARGS},
+#endif /* USE_UNICODE_WCHAR_CACHE */
     {"test_widechar",           test_widechar,                   METH_NOARGS},
     {"unicode_aswidechar",      unicode_aswidechar,              METH_VARARGS},
     {"unicode_aswidecharstring",unicode_aswidecharstring,        METH_VARARGS},
@@ -5408,9 +5420,11 @@ static PyMethodDef TestMethods[] = {
     {"unicode_asutf8andsize",   unicode_asutf8andsize,           METH_VARARGS},
     {"unicode_findchar",        unicode_findchar,                METH_VARARGS},
     {"unicode_copycharacters",  unicode_copycharacters,          METH_VARARGS},
+#if USE_UNICODE_WCHAR_CACHE
     {"unicode_encodedecimal",   unicode_encodedecimal,           METH_VARARGS},
     {"unicode_transformdecimaltoascii", unicode_transformdecimaltoascii, METH_VARARGS},
     {"unicode_legacy_string",   unicode_legacy_string,           METH_VARARGS},
+#endif /* USE_UNICODE_WCHAR_CACHE */
     {"_test_thread_state",      test_thread_state,               METH_VARARGS},
     {"_pending_threadfunc",     pending_threadfunc,              METH_VARARGS},
 #ifdef HAVE_GETTIMEOFDAY
diff --git a/Modules/_winapi.c b/Modules/_winapi.c
index e1672c47852..ddb11aa5a82 100644
--- a/Modules/_winapi.c
+++ b/Modules/_winapi.c
@@ -164,10 +164,11 @@ create_converter('LPCVOID', '" F_POINTER "')
 create_converter('BOOL', 'i') # F_BOOL used previously (always 'i')
 create_converter('DWORD', 'k') # F_DWORD is always "k" (which is much shorter)
 create_converter('LPCTSTR', 's')
-create_converter('LPCWSTR', 'u')
-create_converter('LPWSTR', 'u')
 create_converter('UINT', 'I') # F_UINT used previously (always 'I')
 
+class LPCWSTR_converter(Py_UNICODE_converter):
+    type = 'LPCWSTR'
+
 class HANDLE_return_converter(CReturnConverter):
     type = 'HANDLE'
 
@@ -197,7 +198,7 @@ class LPVOID_return_converter(CReturnConverter):
         data.return_conversion.append(
             'return_value = HANDLE_TO_PYNUM(_return_value);\n')
 [python start generated code]*/
-/*[python end generated code: output=da39a3ee5e6b4b0d input=79464c61a31ae932]*/
+/*[python end generated code: output=da39a3ee5e6b4b0d input=011ee0c3a2244bfe]*/
 
 #include "clinic/_winapi.c.h"
 
@@ -520,15 +521,15 @@ _winapi_CreateFileMapping_impl(PyObject *module, HANDLE file_handle,
 /*[clinic input]
 _winapi.CreateJunction
 
-    src_path: LPWSTR
-    dst_path: LPWSTR
+    src_path: LPCWSTR
+    dst_path: LPCWSTR
     /
 [clinic start generated code]*/
 
 static PyObject *
-_winapi_CreateJunction_impl(PyObject *module, LPWSTR src_path,
-                            LPWSTR dst_path)
-/*[clinic end generated code: output=66b7eb746e1dfa25 input=8cd1f9964b6e3d36]*/
+_winapi_CreateJunction_impl(PyObject *module, LPCWSTR src_path,
+                            LPCWSTR dst_path)
+/*[clinic end generated code: output=44b3f5e9bbcc4271 input=963d29b44b9384a7]*/
 {
     /* Privilege adjustment */
     HANDLE token = NULL;
diff --git a/Modules/clinic/_winapi.c.h b/Modules/clinic/_winapi.c.h
index 6022dfe0db4..a9630d55998 100644
--- a/Modules/clinic/_winapi.c.h
+++ b/Modules/clinic/_winapi.c.h
@@ -195,8 +195,8 @@ _winapi_CreateFileMapping(PyObject *module, PyObject *const *args, Py_ssize_t na
     LPCWSTR name;
     HANDLE _return_value;
 
-    if (!_PyArg_ParseStack(args, nargs, "" F_HANDLE "" F_POINTER "kkku:CreateFileMapping",
-        &file_handle, &security_attributes, &protect, &max_size_high, &max_size_low, &name)) {
+    if (!_PyArg_ParseStack(args, nargs, "" F_HANDLE "" F_POINTER "kkkO&:CreateFileMapping",
+        &file_handle, &security_attributes, &protect, &max_size_high, &max_size_low, _PyUnicode_WideCharString_Converter, &name)) {
         goto exit;
     }
     _return_value = _winapi_CreateFileMapping_impl(module, file_handle, security_attributes, protect, max_size_high, max_size_low, name);
@@ -209,6 +209,11 @@ _winapi_CreateFileMapping(PyObject *module, PyObject *const *args, Py_ssize_t na
     return_value = HANDLE_TO_PYNUM(_return_value);
 
 exit:
+    /* Cleanup for name */
+    #if !USE_UNICODE_WCHAR_CACHE
+    PyMem_Free((void *)name);
+    #endif /* USE_UNICODE_WCHAR_CACHE */
+
     return return_value;
 }
 
@@ -221,23 +226,55 @@ PyDoc_STRVAR(_winapi_CreateJunction__doc__,
     {"CreateJunction", (PyCFunction)(void(*)(void))_winapi_CreateJunction, METH_FASTCALL, _winapi_CreateJunction__doc__},
 
 static PyObject *
-_winapi_CreateJunction_impl(PyObject *module, LPWSTR src_path,
-                            LPWSTR dst_path);
+_winapi_CreateJunction_impl(PyObject *module, LPCWSTR src_path,
+                            LPCWSTR dst_path);
 
 static PyObject *
 _winapi_CreateJunction(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 {
     PyObject *return_value = NULL;
-    LPWSTR src_path;
-    LPWSTR dst_path;
+    LPCWSTR src_path;
+    LPCWSTR dst_path;
 
-    if (!_PyArg_ParseStack(args, nargs, "uu:CreateJunction",
-        &src_path, &dst_path)) {
+    if (!_PyArg_CheckPositional("CreateJunction", nargs, 2, 2)) {
+        goto exit;
+    }
+    if (!PyUnicode_Check(args[0])) {
+        _PyArg_BadArgument("CreateJunction", "argument 1", "str", args[0]);
+        goto exit;
+    }
+    #if USE_UNICODE_WCHAR_CACHE
+    src_path = _PyUnicode_AsUnicode(args[0]);
+    #else /* USE_UNICODE_WCHAR_CACHE */
+    src_path = PyUnicode_AsWideCharString(args[0], NULL);
+    #endif /* USE_UNICODE_WCHAR_CACHE */
+    if (src_path == NULL) {
+        goto exit;
+    }
+    if (!PyUnicode_Check(args[1])) {
+        _PyArg_BadArgument("CreateJunction", "argument 2", "str", args[1]);
+        goto exit;
+    }
+    #if USE_UNICODE_WCHAR_CACHE
+    dst_path = _PyUnicode_AsUnicode(args[1]);
+    #else /* USE_UNICODE_WCHAR_CACHE */
+    dst_path = PyUnicode_AsWideCharString(args[1], NULL);
+    #endif /* USE_UNICODE_WCHAR_CACHE */
+    if (dst_path == NULL) {
         goto exit;
     }
     return_value = _winapi_CreateJunction_impl(module, src_path, dst_path);
 
 exit:
+    /* Cleanup for src_path */
+    #if !USE_UNICODE_WCHAR_CACHE
+    PyMem_Free((void *)src_path);
+    #endif /* USE_UNICODE_WCHAR_CACHE */
+    /* Cleanup for dst_path */
+    #if !USE_UNICODE_WCHAR_CACHE
+    PyMem_Free((void *)dst_path);
+    #endif /* USE_UNICODE_WCHAR_CACHE */
+
     return return_value;
 }
 
@@ -715,8 +752,8 @@ _winapi_OpenFileMapping(PyObject *module, PyObject *const *args, Py_ssize_t narg
     LPCWSTR name;
     HANDLE _return_value;
 
-    if (!_PyArg_ParseStack(args, nargs, "kiu:OpenFileMapping",
-        &desired_access, &inherit_handle, &name)) {
+    if (!_PyArg_ParseStack(args, nargs, "kiO&:OpenFileMapping",
+        &desired_access, &inherit_handle, _PyUnicode_WideCharString_Converter, &name)) {
         goto exit;
     }
     _return_value = _winapi_OpenFileMapping_impl(module, desired_access, inherit_handle, name);
@@ -729,6 +766,11 @@ _winapi_OpenFileMapping(PyObject *module, PyObject *const *args, Py_ssize_t narg
     return_value = HANDLE_TO_PYNUM(_return_value);
 
 exit:
+    /* Cleanup for name */
+    #if !USE_UNICODE_WCHAR_CACHE
+    PyMem_Free((void *)name);
+    #endif /* USE_UNICODE_WCHAR_CACHE */
+
     return return_value;
 }
 
@@ -1106,4 +1148,4 @@ _winapi_GetFileType(PyObject *module, PyObject *const *args, Py_ssize_t nargs, P
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=db87076a32fa7abe input=a9049054013a1b77]*/
+/*[clinic end generated code: output=1f10e03f64ff9777 input=a9049054013a1b77]*/
diff --git a/Modules/overlapped.c b/Modules/overlapped.c
index 9c4e2da9dfb..4f0ba85d798 100644
--- a/Modules/overlapped.c
+++ b/Modules/overlapped.c
@@ -1291,6 +1291,7 @@ _overlapped_Overlapped_AcceptEx_impl(OverlappedObject *self,
 static int
 parse_address(PyObject *obj, SOCKADDR *Address, int Length)
 {
+    PyObject *Host_obj;
     Py_UNICODE *Host;
     unsigned short Port;
     unsigned long FlowInfo;
@@ -1298,33 +1299,66 @@ parse_address(PyObject *obj, SOCKADDR *Address, int Length)
 
     memset(Address, 0, Length);
 
-    if (PyArg_ParseTuple(obj, "uH", &Host, &Port))
-    {
+    switch (PyTuple_GET_SIZE(obj)) {
+    case 2: {
+        if (!PyArg_ParseTuple(obj, "UH", &Host_obj, &Port)) {
+            return -1;
+        }
+#if USE_UNICODE_WCHAR_CACHE
+        Host = (wchar_t *)_PyUnicode_AsUnicode(Host_obj);
+#else /* USE_UNICODE_WCHAR_CACHE */
+        Host = PyUnicode_AsWideCharString(Host_obj, NULL);
+#endif /* USE_UNICODE_WCHAR_CACHE */
+        if (Host == NULL) {
+            return -1;
+        }
         Address->sa_family = AF_INET;
         if (WSAStringToAddressW(Host, AF_INET, NULL, Address, &Length) < 0) {
             SetFromWindowsErr(WSAGetLastError());
-            return -1;
+            Length = -1;
+        }
+        else {
+            ((SOCKADDR_IN*)Address)->sin_port = htons(Port);
         }
-        ((SOCKADDR_IN*)Address)->sin_port = htons(Port);
+#if !USE_UNICODE_WCHAR_CACHE
+        PyMem_Free(Host);
+#endif /* USE_UNICODE_WCHAR_CACHE */
         return Length;
     }
-    else if (PyArg_ParseTuple(obj,
-                              "uHkk;ConnectEx(): illegal address_as_bytes "
-                              "argument", &Host, &Port, &FlowInfo, &ScopeId))
-    {
-        PyErr_Clear();
+    case 4: {
+        if (!PyArg_ParseTuple(obj,
+                "UHkk;ConnectEx(): illegal address_as_bytes argument",
+                &Host_obj, &Port, &FlowInfo, &ScopeId))
+        {
+            return -1;
+        }
+#if USE_UNICODE_WCHAR_CACHE
+        Host = (wchar_t *)_PyUnicode_AsUnicode(Host_obj);
+#else /* USE_UNICODE_WCHAR_CACHE */
+        Host = PyUnicode_AsWideCharString(Host_obj, NULL);
+#endif /* USE_UNICODE_WCHAR_CACHE */
+        if (Host == NULL) {
+            return -1;
+        }
         Address->sa_family = AF_INET6;
         if (WSAStringToAddressW(Host, AF_INET6, NULL, Address, &Length) < 0) {
             SetFromWindowsErr(WSAGetLastError());
-            return -1;
+            Length = -1;
+        }
+        else {
+            ((SOCKADDR_IN6*)Address)->sin6_port = htons(Port);
+            ((SOCKADDR_IN6*)Address)->sin6_flowinfo = FlowInfo;
+            ((SOCKADDR_IN6*)Address)->sin6_scope_id = ScopeId;
         }
-        ((SOCKADDR_IN6*)Address)->sin6_port = htons(Port);
-        ((SOCKADDR_IN6*)Address)->sin6_flowinfo = FlowInfo;
-        ((SOCKADDR_IN6*)Address)->sin6_scope_id = ScopeId;
+#if !USE_UNICODE_WCHAR_CACHE
+        PyMem_Free(Host);
+#endif /* USE_UNICODE_WCHAR_CACHE */
         return Length;
     }
-
-    return -1;
+    default:
+        PyErr_SetString(PyExc_ValueError, "illegal address_as_bytes argument");
+        return -1;
+    }
 }
 
 /*[clinic input]
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index a411f28987e..efd99544f5a 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -988,6 +988,11 @@ typedef struct {
 static void
 path_cleanup(path_t *path)
 {
+#if !USE_UNICODE_WCHAR_CACHE
+    wchar_t *wide = (wchar_t *)path->wide;
+    path->wide = NULL;
+    PyMem_Free(wide);
+#endif /* USE_UNICODE_WCHAR_CACHE */
     Py_CLEAR(path->object);
     Py_CLEAR(path->cleanup);
 }
@@ -1002,7 +1007,7 @@ path_converter(PyObject *o, void *p)
     const char *narrow;
 #ifdef MS_WINDOWS
     PyObject *wo = NULL;
-    const wchar_t *wide;
+    wchar_t *wide = NULL;
 #endif
 
 #define FORMAT_EXCEPTION(exc, fmt) \
@@ -1075,7 +1080,14 @@ path_converter(PyObject *o, void *p)
 
     if (is_unicode) {
 #ifdef MS_WINDOWS
+#if USE_UNICODE_WCHAR_CACHE
+_Py_COMP_DIAG_PUSH
+_Py_COMP_DIAG_IGNORE_DEPR_DECLS
         wide = PyUnicode_AsUnicodeAndSize(o, &length);
+_Py_COMP_DIAG_POP
+#else /* USE_UNICODE_WCHAR_CACHE */
+        wide = PyUnicode_AsWideCharString(o, &length);
+#endif /* USE_UNICODE_WCHAR_CACHE */
         if (!wide) {
             goto error_exit;
         }
@@ -1091,6 +1103,9 @@ path_converter(PyObject *o, void *p)
         path->wide = wide;
         path->narrow = FALSE;
         path->fd = -1;
+#if !USE_UNICODE_WCHAR_CACHE
+        wide = NULL;
+#endif /* USE_UNICODE_WCHAR_CACHE */
         goto success_exit;
 #else
         if (!PyUnicode_FSConverter(o, &bytes)) {
@@ -1166,7 +1181,15 @@ path_converter(PyObject *o, void *p)
         goto error_exit;
     }
 
+#if USE_UNICODE_WCHAR_CACHE
+_Py_COMP_DIAG_PUSH
+_Py_COMP_DIAG_IGNORE_DEPR_DECLS
     wide = PyUnicode_AsUnicodeAndSize(wo, &length);
+_Py_COMP_DIAG_POP
+#else /* USE_UNICODE_WCHAR_CACHE */
+    wide = PyUnicode_AsWideCharString(wo, &length);
+    Py_DECREF(wo);
+#endif /* USE_UNICODE_WCHAR_CACHE */
     if (!wide) {
         goto error_exit;
     }
@@ -1180,8 +1203,12 @@ path_converter(PyObject *o, void *p)
     }
     path->wide = wide;
     path->narrow = TRUE;
-    path->cleanup = wo;
     Py_DECREF(bytes);
+#if USE_UNICODE_WCHAR_CACHE
+    path->cleanup = wo;
+#else /* USE_UNICODE_WCHAR_CACHE */
+    wide = NULL;
+#endif /* USE_UNICODE_WCHAR_CACHE */
 #else
     path->wide = NULL;
     path->narrow = narrow;
@@ -1205,7 +1232,11 @@ path_converter(PyObject *o, void *p)
     Py_XDECREF(o);
     Py_XDECREF(bytes);
 #ifdef MS_WINDOWS
+#if USE_UNICODE_WCHAR_CACHE
     Py_XDECREF(wo);
+#else /* USE_UNICODE_WCHAR_CACHE */
+    PyMem_Free(wide);
+#endif /* USE_UNICODE_WCHAR_CACHE */
 #endif
     return 0;
 }
@@ -12824,7 +12855,15 @@ DirEntry_fetch_stat(PyObject *module, DirEntry *self, int follow_symlinks)
 #ifdef MS_WINDOWS
     if (!PyUnicode_FSDecoder(self->path, &ub))
         return NULL;
+#if USE_UNICODE_WCHAR_CACHE
+_Py_COMP_DIAG_PUSH
+_Py_COMP_DIAG_IGNORE_DEPR_DECLS
     const wchar_t *path = PyUnicode_AsUnicode(ub);
+_Py_COMP_DIAG_POP
+#else /* USE_UNICODE_WCHAR_CACHE */
+    wchar_t *path = PyUnicode_AsWideCharString(ub, NULL);
+    Py_DECREF(ub);
+#endif /* USE_UNICODE_WCHAR_CACHE */
 #else /* POSIX */
     if (!PyUnicode_FSConverter(self->path, &ub))
         return NULL;
@@ -12834,6 +12873,7 @@ DirEntry_fetch_stat(PyObject *module, DirEntry *self, int follow_symlinks)
         result = fstatat(self->dir_fd, path, &st,
                          follow_symlinks ? 0 : AT_SYMLINK_NOFOLLOW);
 #else
+        Py_DECREF(ub);
         PyErr_SetString(PyExc_NotImplementedError, "can't fetch stat");
         return NULL;
 #endif /* HAVE_FSTATAT */
@@ -12846,7 +12886,11 @@ DirEntry_fetch_stat(PyObject *module, DirEntry *self, int follow_symlinks)
         else
             result = LSTAT(path, &st);
     }
+#if defined(MS_WINDOWS) && !USE_UNICODE_WCHAR_CACHE
+    PyMem_Free(path);
+#else /* USE_UNICODE_WCHAR_CACHE */
     Py_DECREF(ub);
+#endif /* USE_UNICODE_WCHAR_CACHE */
 
     if (result != 0)
         return path_object_error(self->path);
@@ -13035,15 +13079,24 @@ os_DirEntry_inode_impl(DirEntry *self)
 #ifdef MS_WINDOWS
     if (!self->got_file_index) {
         PyObject *unicode;
-        const wchar_t *path;
         STRUCT_STAT stat;
         int result;
 
         if (!PyUnicode_FSDecoder(self->path, &unicode))
             return NULL;
-        path = PyUnicode_AsUnicode(unicode);
+#if USE_UNICODE_WCHAR_CACHE
+_Py_COMP_DIAG_PUSH
+_Py_COMP_DIAG_IGNORE_DEPR_DECLS
+        const wchar_t *path = PyUnicode_AsUnicode(unicode);
         result = LSTAT(path, &stat);
         Py_DECREF(unicode);
+_Py_COMP_DIAG_POP
+#else /* USE_UNICODE_WCHAR_CACHE */
+        wchar_t *path = PyUnicode_AsWideCharString(unicode, NULL);
+        Py_DECREF(unicode);
+        result = LSTAT(path, &stat);
+        PyMem_Free(path);
+#endif /* USE_UNICODE_WCHAR_CACHE */
 
         if (result != 0)
             return path_object_error(self->path);
@@ -13597,10 +13650,9 @@ os_scandir_impl(PyObject *module, path_t *path)
     iterator->dirp = NULL;
 #endif
 
-    memcpy(&iterator->path, path, sizeof(path_t));
     /* Move the ownership to iterator->path */
-    path->object = NULL;
-    path->cleanup = NULL;
+    memcpy(&iterator->path, path, sizeof(path_t));
+    memset(path, 0, sizeof(path_t));
 
 #ifdef MS_WINDOWS
     iterator->first_time = 1;
@@ -13622,9 +13674,9 @@ os_scandir_impl(PyObject *module, path_t *path)
 #else /* POSIX */
     errno = 0;
 #ifdef HAVE_FDOPENDIR
-    if (path->fd != -1) {
+    if (iterator->path.fd != -1) {
         /* closedir() closes the FD, so we duplicate it */
-        fd = _Py_dup(path->fd);
+        fd = _Py_dup(iterator->path.fd);
         if (fd == -1)
             goto error;
 
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 648dd15ca09..2e1045ad3a7 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -3150,9 +3150,11 @@ unicode_get_widechar_size(PyObject *unicode)
     assert(unicode != NULL);
     assert(_PyUnicode_CHECK(unicode));
 
+#if USE_UNICODE_WCHAR_CACHE
     if (_PyUnicode_WSTR(unicode) != NULL) {
         return PyUnicode_WSTR_LENGTH(unicode);
     }
+#endif /* USE_UNICODE_WCHAR_CACHE */
     assert(PyUnicode_IS_READY(unicode));
 
     res = _PyUnicode_LENGTH(unicode);
@@ -3173,16 +3175,21 @@ unicode_get_widechar_size(PyObject *unicode)
 static void
 unicode_copy_as_widechar(PyObject *unicode, wchar_t *w, Py_ssize_t size)
 {
-    const wchar_t *wstr;
-
     assert(unicode != NULL);
     assert(_PyUnicode_CHECK(unicode));
 
-    wstr = _PyUnicode_WSTR(unicode);
+#if USE_UNICODE_WCHAR_CACHE
+    const wchar_t *wstr = _PyUnicode_WSTR(unicode);
     if (wstr != NULL) {
         memcpy(w, wstr, size * sizeof(wchar_t));
         return;
     }
+#else /* USE_UNICODE_WCHAR_CACHE */
+    if (PyUnicode_KIND(unicode) == sizeof(wchar_t)) {
+        memcpy(w, PyUnicode_DATA(unicode), size * sizeof(wchar_t));
+        return;
+    }
+#endif /* USE_UNICODE_WCHAR_CACHE */
     assert(PyUnicode_IS_READY(unicode));
 
     if (PyUnicode_KIND(unicode) == PyUnicode_1BYTE_KIND) {
@@ -4378,7 +4385,6 @@ unicode_decode_call_errorhandler_wchar(
     Py_ssize_t requiredsize;
     Py_ssize_t newpos;
     PyObject *inputobj = NULL;
-    wchar_t *repwstr;
     Py_ssize_t repwlen;
 
     if (*errorHandler == NULL) {
@@ -4424,9 +4430,19 @@ unicode_decode_call_errorhandler_wchar(
         goto onError;
     }
 
-    repwstr = PyUnicode_AsUnicodeAndSize(repunicode, &repwlen);
-    if (repwstr == NULL)
+#if USE_UNICODE_WCHAR_CACHE
+_Py_COMP_DIAG_PUSH
+_Py_COMP_DIAG_IGNORE_DEPR_DECLS
+    repwlen = PyUnicode_GetSize(repunicode);
+    if (repwlen < 0)
+        goto onError;
+_Py_COMP_DIAG_POP
+#else /* USE_UNICODE_WCHAR_CACHE */
+    repwlen = PyUnicode_AsWideChar(repunicode, NULL, 0);
+    if (repwlen < 0)
         goto onError;
+    repwlen--;
+#endif /* USE_UNICODE_WCHAR_CACHE */
     /* need more space? (at least enough for what we
        have+the replacement+the rest of the string (starting
        at the new input position), so we won't have to check space
@@ -4446,7 +4462,7 @@ unicode_decode_call_errorhandler_wchar(
             goto onError;
         }
     }
-    wcsncpy(*buf + *outpos, repwstr, repwlen);
+    PyUnicode_AsWideChar(repunicode, *buf + *outpos, repwlen);
     *outpos += repwlen;
     *endinpos = newpos;
     *inptr = *input + newpos;
@@ -7748,6 +7764,7 @@ encode_code_page_strict(UINT code_page, PyObject **outbytes,
     /* Create a substring so that we can get the UTF-16 representation
        of just the slice under consideration. */
     PyObject *substring;
+    int ret = -1;
 
     assert(len > 0);
 
@@ -7759,11 +7776,22 @@ encode_code_page_strict(UINT code_page, PyObject **outbytes,
     substring = PyUnicode_Substring(unicode, offset, offset+len);
     if (substring == NULL)
         return -1;
+#if USE_UNICODE_WCHAR_CACHE
+_Py_COMP_DIAG_PUSH
+_Py_COMP_DIAG_IGNORE_DEPR_DECLS
     p = PyUnicode_AsUnicodeAndSize(substring, &size);
     if (p == NULL) {
         Py_DECREF(substring);
         return -1;
     }
+_Py_COMP_DIAG_POP
+#else /* USE_UNICODE_WCHAR_CACHE */
+    p = PyUnicode_AsWideCharString(substring, &size);
+    Py_CLEAR(substring);
+    if (p == NULL) {
+        return -1;
+    }
+#endif /* USE_UNICODE_WCHAR_CACHE */
     assert(size <= INT_MAX);
 
     /* First get the size of the result */
@@ -7775,16 +7803,15 @@ encode_code_page_strict(UINT code_page, PyObject **outbytes,
         goto error;
     /* If we used a default char, then we failed! */
     if (pusedDefaultChar && *pusedDefaultChar) {
-        Py_DECREF(substring);
-        return -2;
+        ret = -2;
+        goto done;
     }
 
     if (*outbytes == NULL) {
         /* Create string object */
         *outbytes = PyBytes_FromStringAndSize(NULL, outsize);
         if (*outbytes == NULL) {
-            Py_DECREF(substring);
-            return -1;
+            goto done;
         }
         out = PyBytes_AS_STRING(*outbytes);
     }
@@ -7793,12 +7820,10 @@ encode_code_page_strict(UINT code_page, PyObject **outbytes,
         const Py_ssize_t n = PyBytes_Size(*outbytes);
         if (outsize > PY_SSIZE_T_MAX - n) {
             PyErr_NoMemory();
-            Py_DECREF(substring);
-            return -1;
+            goto done;
         }
         if (_PyBytes_Resize(outbytes, n + outsize) < 0) {
-            Py_DECREF(substring);
-            return -1;
+            goto done;
         }
         out = PyBytes_AS_STRING(*outbytes) + n;
     }
@@ -7808,19 +7833,29 @@ encode_code_page_strict(UINT code_page, PyObject **outbytes,
                                   p, (int)size,
                                   out, outsize,
                                   NULL, pusedDefaultChar);
-    Py_CLEAR(substring);
     if (outsize <= 0)
         goto error;
-    if (pusedDefaultChar && *pusedDefaultChar)
-        return -2;
-    return 0;
+    if (pusedDefaultChar && *pusedDefaultChar) {
+        ret = -2;
+        goto done;
+    }
+    ret = 0;
+
+done:
+#if USE_UNICODE_WCHAR_CACHE
+    Py_DECREF(substring);
+#else /* USE_UNICODE_WCHAR_CACHE */
+    PyMem_Free(p);
+#endif /* USE_UNICODE_WCHAR_CACHE */
+    return ret;
 
 error:
-    Py_XDECREF(substring);
-    if (GetLastError() == ERROR_NO_UNICODE_TRANSLATION)
-        return -2;
+    if (GetLastError() == ERROR_NO_UNICODE_TRANSLATION) {
+        ret = -2;
+        goto done;
+    }
     PyErr_SetFromWindowsErr(0);
-    return -1;
+    goto done;
 }
 
 /*
diff --git a/PC/clinic/winreg.c.h b/PC/clinic/winreg.c.h
index 3301bed9713..183301f0618 100644
--- a/PC/clinic/winreg.c.h
+++ b/PC/clinic/winreg.c.h
@@ -1143,8 +1143,7 @@ PyDoc_STRVAR(winreg_SetValue__doc__,
 
 static PyObject *
 winreg_SetValue_impl(PyObject *module, HKEY key, const Py_UNICODE *sub_key,
-                     DWORD type, const Py_UNICODE *value,
-                     Py_ssize_clean_t value_length);
+                     DWORD type, PyObject *value_obj);
 
 static PyObject *
 winreg_SetValue(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
@@ -1153,14 +1152,13 @@ winreg_SetValue(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
     HKEY key;
     const Py_UNICODE *sub_key;
     DWORD type;
-    const Py_UNICODE *value;
-    Py_ssize_clean_t value_length;
+    PyObject *value_obj;
 
-    if (!_PyArg_ParseStack(args, nargs, "O&O&ku#:SetValue",
-        clinic_HKEY_converter, &key, _PyUnicode_WideCharString_Opt_Converter, &sub_key, &type, &value, &value_length)) {
+    if (!_PyArg_ParseStack(args, nargs, "O&O&kU:SetValue",
+        clinic_HKEY_converter, &key, _PyUnicode_WideCharString_Opt_Converter, &sub_key, &type, &value_obj)) {
         goto exit;
     }
-    return_value = winreg_SetValue_impl(module, key, sub_key, type, value, value_length);
+    return_value = winreg_SetValue_impl(module, key, sub_key, type, value_obj);
 
 exit:
     /* Cleanup for sub_key */
@@ -1348,4 +1346,4 @@ winreg_QueryReflectionKey(PyObject *module, PyObject *arg)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=30b1311886c13907 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=497a2e804821d5c9 input=a9049054013a1b77]*/
diff --git a/PC/winreg.c b/PC/winreg.c
index b2725b857d0..a24d784c773 100644
--- a/PC/winreg.c
+++ b/PC/winreg.c
@@ -640,16 +640,25 @@ Py2Reg(PyObject *value, DWORD typ, BYTE **retDataBuf, DWORD *retDataSize)
                 for (j = 0; j < i; j++)
                 {
                     PyObject *t;
-                    wchar_t *wstr;
                     Py_ssize_t len;
 
                     t = PyList_GET_ITEM(value, j);
                     if (!PyUnicode_Check(t))
                         return FALSE;
-                    wstr = PyUnicode_AsUnicodeAndSize(t, &len);
-                    if (wstr == NULL)
+#if USE_UNICODE_WCHAR_CACHE
+_Py_COMP_DIAG_PUSH
+_Py_COMP_DIAG_IGNORE_DEPR_DECLS
+                    len = PyUnicode_GetSize(t);
+                    if (len < 0)
                         return FALSE;
-                    size += Py_SAFE_DOWNCAST((len + 1) * sizeof(wchar_t),
+                    len++;
+_Py_COMP_DIAG_POP
+#else /* USE_UNICODE_WCHAR_CACHE */
+                    len = PyUnicode_AsWideChar(t, NULL, 0);
+                    if (len < 0)
+                        return FALSE;
+#endif /* USE_UNICODE_WCHAR_CACHE */
+                    size += Py_SAFE_DOWNCAST(len * sizeof(wchar_t),
                                              size_t, DWORD);
                 }
 
@@ -665,17 +674,18 @@ Py2Reg(PyObject *value, DWORD typ, BYTE **retDataBuf, DWORD *retDataSize)
                 for (j = 0; j < i; j++)
                 {
                     PyObject *t;
-                    wchar_t *wstr;
                     Py_ssize_t len;
 
                     t = PyList_GET_ITEM(value, j);
-                    wstr = PyUnicode_AsUnicodeAndSize(t, &len);
-                    assert(wstr);
-                    wcscpy(P, wstr);
-                    P += (len + 1);
+                    assert(size > 0);
+                    len = PyUnicode_AsWideChar(t, P, size);
+                    assert(len >= 0);
+                    assert(len < size);
+                    size -= (DWORD)len + 1;
+                    P += len + 1;
                 }
                 /* And doubly-terminate the list... */
-                *P = '\0';
+                *P = L'\0';
                 break;
             }
         case REG_BINARY:
@@ -1669,7 +1679,7 @@ winreg.SetValue
     type: DWORD
         An integer that specifies the type of the data.  Currently this must
         be REG_SZ, meaning only strings are supported.
-    value: Py_UNICODE(zeroes=True)
+    value as value_obj: unicode
         A string that specifies the new value.
     /
 
@@ -1688,30 +1698,51 @@ KEY_SET_VALUE access.
 
 static PyObject *
 winreg_SetValue_impl(PyObject *module, HKEY key, const Py_UNICODE *sub_key,
-                     DWORD type, const Py_UNICODE *value,
-                     Py_ssize_clean_t value_length)
-/*[clinic end generated code: output=686bedb1cbb4367b input=2cd2adab79339c53]*/
+                     DWORD type, PyObject *value_obj)
+/*[clinic end generated code: output=d4773dc9c372311a input=bf088494ae2d24fd]*/
 {
+    Py_ssize_t value_length;
     long rc;
 
     if (type != REG_SZ) {
         PyErr_SetString(PyExc_TypeError, "type must be winreg.REG_SZ");
         return NULL;
     }
-    if ((size_t)value_length >= PY_DWORD_MAX) {
+
+#if USE_UNICODE_WCHAR_CACHE
+_Py_COMP_DIAG_PUSH
+_Py_COMP_DIAG_IGNORE_DEPR_DECLS
+    const wchar_t *value = PyUnicode_AsUnicodeAndSize(value_obj, &value_length);
+_Py_COMP_DIAG_POP
+#else /* USE_UNICODE_WCHAR_CACHE */
+    wchar_t *value = PyUnicode_AsWideCharString(value_obj, &value_length);
+#endif /* USE_UNICODE_WCHAR_CACHE */
+    if (value == NULL) {
+        return NULL;
+    }
+    if ((Py_ssize_t)(DWORD)value_length != value_length) {
         PyErr_SetString(PyExc_OverflowError, "value is too long");
+#if !USE_UNICODE_WCHAR_CACHE
+        PyMem_Free(value);
+#endif /* USE_UNICODE_WCHAR_CACHE */
         return NULL;
     }
 
     if (PySys_Audit("winreg.SetValue", "nunu#",
                     (Py_ssize_t)key, sub_key, (Py_ssize_t)type,
                     value, value_length) < 0) {
+#if !USE_UNICODE_WCHAR_CACHE
+        PyMem_Free(value);
+#endif /* USE_UNICODE_WCHAR_CACHE */
         return NULL;
     }
 
     Py_BEGIN_ALLOW_THREADS
     rc = RegSetValueW(key, sub_key, REG_SZ, value, (DWORD)(value_length + 1));
     Py_END_ALLOW_THREADS
+#if !USE_UNICODE_WCHAR_CACHE
+    PyMem_Free(value);
+#endif /* USE_UNICODE_WCHAR_CACHE */
     if (rc != ERROR_SUCCESS)
         return PyErr_SetFromWindowsErrWithFunction(rc, "RegSetValue");
     Py_RETURN_NONE;
diff --git a/Python/dynload_win.c b/Python/dynload_win.c
index 8431c5b3b2f..5702ab2cd71 100644
--- a/Python/dynload_win.c
+++ b/Python/dynload_win.c
@@ -166,11 +166,14 @@ dl_funcptr _PyImport_FindSharedFuncptrWindows(const char *prefix,
 {
     dl_funcptr p;
     char funcname[258], *import_python;
-    const wchar_t *wpathname;
 
     _Py_CheckPython3();
 
-    wpathname = _PyUnicode_AsUnicode(pathname);
+#if USE_UNICODE_WCHAR_CACHE
+    const wchar_t *wpathname = _PyUnicode_AsUnicode(pathname);
+#else /* USE_UNICODE_WCHAR_CACHE */
+    wchar_t *wpathname = PyUnicode_AsWideCharString(pathname, NULL);
+#endif /* USE_UNICODE_WCHAR_CACHE */
     if (wpathname == NULL)
         return NULL;
 
@@ -192,6 +195,9 @@ dl_funcptr _PyImport_FindSharedFuncptrWindows(const char *prefix,
                               LOAD_LIBRARY_SEARCH_DEFAULT_DIRS |
                               LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR);
         Py_END_ALLOW_THREADS
+#if !USE_UNICODE_WCHAR_CACHE
+        PyMem_Free(wpathname);
+#endif /* USE_UNICODE_WCHAR_CACHE */
 
         /* restore old error mode settings */
         SetErrorMode(old_mode);
diff --git a/Python/fileutils.c b/Python/fileutils.c
index 2c86828ba98..50ef3c174ac 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -1008,15 +1008,21 @@ _Py_stat(PyObject *path, struct stat *statbuf)
 #ifdef MS_WINDOWS
     int err;
     struct _stat wstatbuf;
-    const wchar_t *wpath;
 
-    wpath = _PyUnicode_AsUnicode(path);
+#if USE_UNICODE_WCHAR_CACHE
+    const wchar_t *wpath = _PyUnicode_AsUnicode(path);
+#else /* USE_UNICODE_WCHAR_CACHE */
+    wchar_t *wpath = PyUnicode_AsWideCharString(path, NULL);
+#endif /* USE_UNICODE_WCHAR_CACHE */
     if (wpath == NULL)
         return -2;
 
     err = _wstat(wpath, &wstatbuf);
     if (!err)
         statbuf->st_mode = wstatbuf.st_mode;
+#if !USE_UNICODE_WCHAR_CACHE
+    PyMem_Free(wpath);
+#endif /* USE_UNICODE_WCHAR_CACHE */
     return err;
 #else
     int ret;
@@ -1433,7 +1439,6 @@ _Py_fopen_obj(PyObject *path, const char *mode)
     FILE *f;
     int async_err = 0;
 #ifdef MS_WINDOWS
-    const wchar_t *wpath;
     wchar_t wmode[10];
     int usize;
 
@@ -1448,7 +1453,11 @@ _Py_fopen_obj(PyObject *path, const char *mode)
                      Py_TYPE(path));
         return NULL;
     }
-    wpath = _PyUnicode_AsUnicode(path);
+#if USE_UNICODE_WCHAR_CACHE
+    const wchar_t *wpath = _PyUnicode_AsUnicode(path);
+#else /* USE_UNICODE_WCHAR_CACHE */
+    wchar_t *wpath = PyUnicode_AsWideCharString(path, NULL);
+#endif /* USE_UNICODE_WCHAR_CACHE */
     if (wpath == NULL)
         return NULL;
 
@@ -1456,6 +1465,9 @@ _Py_fopen_obj(PyObject *path, const char *mode)
                                 wmode, Py_ARRAY_LENGTH(wmode));
     if (usize == 0) {
         PyErr_SetFromWindowsErr(0);
+#if !USE_UNICODE_WCHAR_CACHE
+        PyMem_Free(wpath);
+#endif /* USE_UNICODE_WCHAR_CACHE */
         return NULL;
     }
 
@@ -1465,6 +1477,9 @@ _Py_fopen_obj(PyObject *path, const char *mode)
         Py_END_ALLOW_THREADS
     } while (f == NULL
              && errno == EINTR && !(async_err = PyErr_CheckSignals()));
+#if !USE_UNICODE_WCHAR_CACHE
+    PyMem_Free(wpath);
+#endif /* USE_UNICODE_WCHAR_CACHE */
 #else
     PyObject *bytes;
     const char *path_bytes;