bpo-45582: Port getpath[p].c to Python (GH-29041)

The getpath.py file is frozen at build time and executed as code over a namespace. It is never imported, nor is it meant to be importable or reusable. However, it should be easier to read, modify, and patch than the previous code.

This commit attempts to preserve every previously tested quirk, but these may be changed in the future to better align platforms.

5 files changed, 354 insertions, 803 deletions

diff --git a/Python/dynload_win.c b/Python/dynload_win.c
index 5702ab2..854b1e6 100644
--- a/Python/dynload_win.c
+++ b/Python/dynload_win.c
@@ -2,6 +2,9 @@
 /* Support for dynamic loading of extension modules */
 
 #include "Python.h"
+#include "pycore_fileutils.h"     // _Py_add_relfile()
+#include "pycore_pathconfig.h"    // _PyPathConfig_ComputeSysPath0()
+#include "pycore_pystate.h"       // _PyInterpreterState_GET()
 
 #ifdef HAVE_DIRECT_H
 #include <direct.h>
@@ -160,6 +163,60 @@ static char *GetPythonImport (HINSTANCE hModule)
     return NULL;
 }
 
+/* Load python3.dll before loading any extension module that might refer
+   to it. That way, we can be sure that always the python3.dll corresponding
+   to this python DLL is loaded, not a python3.dll that might be on the path
+   by chance.
+   Return whether the DLL was found.
+*/
+extern HMODULE PyWin_DLLhModule;
+static int
+_Py_CheckPython3(void)
+{
+    static int python3_checked = 0;
+    static HANDLE hPython3;
+    #define MAXPATHLEN 512
+    wchar_t py3path[MAXPATHLEN+1];
+    if (python3_checked) {
+        return hPython3 != NULL;
+    }
+    python3_checked = 1;
+
+    /* If there is a python3.dll next to the python3y.dll,
+       use that DLL */
+    if (PyWin_DLLhModule && GetModuleFileNameW(PyWin_DLLhModule, py3path, MAXPATHLEN)) {
+        wchar_t *p = wcsrchr(py3path, L'\\');
+        if (p) {
+            wcscpy(p + 1, PY3_DLLNAME);
+            hPython3 = LoadLibraryExW(py3path, NULL, LOAD_LIBRARY_SEARCH_DEFAULT_DIRS);
+            if (hPython3 != NULL) {
+                return 1;
+            }
+        }
+    }
+
+    /* If we can locate python3.dll in our application dir,
+       use that DLL */
+    hPython3 = LoadLibraryExW(PY3_DLLNAME, NULL, LOAD_LIBRARY_SEARCH_APPLICATION_DIR);
+    if (hPython3 != NULL) {
+        return 1;
+    }
+
+    /* For back-compat, also search {sys.prefix}\DLLs, though
+       that has not been a normal install layout for a while */
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    PyConfig *config = (PyConfig*)_PyInterpreterState_GetConfig(interp);
+    assert(config->prefix);
+    if (config->prefix) {
+        wcscpy_s(py3path, MAXPATHLEN, config->prefix);
+        if (py3path[0] && _Py_add_relfile(py3path, L"DLLs\\" PY3_DLLNAME, MAXPATHLEN) >= 0) {
+            hPython3 = LoadLibraryExW(py3path, NULL, LOAD_LIBRARY_SEARCH_DEFAULT_DIRS);
+        }
+    }
+    return hPython3 != NULL;
+    #undef MAXPATHLEN
+}
+
 dl_funcptr _PyImport_FindSharedFuncptrWindows(const char *prefix,
                                               const char *shortname,
                                               PyObject *pathname, FILE *fp)
diff --git a/Python/fileutils.c b/Python/fileutils.c
index ac0046c..cae6b75 100644
--- a/Python/fileutils.c
+++ b/Python/fileutils.c
@@ -2000,13 +2000,28 @@ _Py_wrealpath(const wchar_t *path,
 #endif
 
 
-#ifndef MS_WINDOWS
 int
 _Py_isabs(const wchar_t *path)
 {
+#ifdef MS_WINDOWS
+    const wchar_t *tail;
+    HRESULT hr = PathCchSkipRoot(path, &tail);
+    if (FAILED(hr) || path == tail) {
+        return 0;
+    }
+    if (tail == &path[1] && (path[0] == SEP || path[0] == ALTSEP)) {
+        // Exclude paths with leading SEP
+        return 0;
+    }
+    if (tail == &path[2] && path[1] == L':') {
+        // Exclude drive-relative paths (e.g. C:filename.ext)
+        return 0;
+    }
+    return 1;
+#else
     return (path[0] == SEP);
-}
 #endif
+}
 
 
 /* Get an absolute path.
@@ -2017,6 +2032,22 @@ _Py_isabs(const wchar_t *path)
 int
 _Py_abspath(const wchar_t *path, wchar_t **abspath_p)
 {
+    if (path[0] == '\0' || !wcscmp(path, L".")) {
+        wchar_t cwd[MAXPATHLEN + 1];
+        cwd[Py_ARRAY_LENGTH(cwd) - 1] = 0;
+        if (!_Py_wgetcwd(cwd, Py_ARRAY_LENGTH(cwd) - 1)) {
+            /* unable to get the current directory */
+            return -1;
+        }
+        *abspath_p = _PyMem_RawWcsdup(cwd);
+        return 0;
+    }
+
+    if (_Py_isabs(path)) {
+        *abspath_p = _PyMem_RawWcsdup(path);
+        return 0;
+    }
+
 #ifdef MS_WINDOWS
     wchar_t woutbuf[MAX_PATH], *woutbufp = woutbuf;
     DWORD result;
@@ -2028,7 +2059,7 @@ _Py_abspath(const wchar_t *path, wchar_t **abspath_p)
         return -1;
     }
 
-    if (result > Py_ARRAY_LENGTH(woutbuf)) {
+    if (result >= Py_ARRAY_LENGTH(woutbuf)) {
         if ((size_t)result <= (size_t)PY_SSIZE_T_MAX / sizeof(wchar_t)) {
             woutbufp = PyMem_RawMalloc((size_t)result * sizeof(wchar_t));
         }
@@ -2055,11 +2086,6 @@ _Py_abspath(const wchar_t *path, wchar_t **abspath_p)
     *abspath_p = _PyMem_RawWcsdup(woutbufp);
     return 0;
 #else
-    if (_Py_isabs(path)) {
-        *abspath_p = _PyMem_RawWcsdup(path);
-        return 0;
-    }
-
     wchar_t cwd[MAXPATHLEN + 1];
     cwd[Py_ARRAY_LENGTH(cwd) - 1] = 0;
     if (!_Py_wgetcwd(cwd, Py_ARRAY_LENGTH(cwd) - 1)) {
@@ -2102,7 +2128,8 @@ join_relfile(wchar_t *buffer, size_t bufsize,
              const wchar_t *dirname, const wchar_t *relfile)
 {
 #ifdef MS_WINDOWS
-    if (FAILED(PathCchCombineEx(buffer, bufsize, dirname, relfile, 0))) {
+    if (FAILED(PathCchCombineEx(buffer, bufsize, dirname, relfile, 
+        PATHCCH_ALLOW_LONG_PATHS | PATHCCH_FORCE_ENABLE_LONG_NAME_PROCESS))) {
         return -1;
     }
 #else
@@ -2180,99 +2207,125 @@ _Py_find_basename(const wchar_t *filename)
     return 0;
 }
 
-
-/* Remove navigation elements such as "." and "..".
-
-   This is mostly a C implementation of posixpath.normpath().
-   Return 0 on success.  Return -1 if "orig" is too big for the buffer. */
-int
-_Py_normalize_path(const wchar_t *path, wchar_t *buf, const size_t buf_len)
+/* In-place path normalisation. Returns the start of the normalized
+   path, which will be within the original buffer. Guaranteed to not
+   make the path longer, and will not fail. 'size' is the length of
+   the path, if known. If -1, the first null character will be assumed
+   to be the end of the path. */
+wchar_t *
+_Py_normpath(wchar_t *path, Py_ssize_t size)
 {
-    assert(path && *path != L'\0');
-    assert(*path == SEP);  // an absolute path
-    if (wcslen(path) + 1 >= buf_len) {
-        return -1;
+    if (!path[0] || size == 0) {
+        return path;
     }
+    wchar_t lastC = L'\0';
+    wchar_t *p1 = path;
+    wchar_t *pEnd = size >= 0 ? &path[size] : NULL;
+    wchar_t *p2 = path;
+    wchar_t *minP2 = path;
 
-    int dots = -1;
-    int check_leading = 1;
-    const wchar_t *buf_start = buf;
-    wchar_t *buf_next = buf;
-    // The resulting filename will never be longer than path.
-    for (const wchar_t *remainder = path; *remainder != L'\0'; remainder++) {
-        wchar_t c = *remainder;
-        buf_next[0] = c;
-        buf_next++;
-        if (c == SEP) {
-            assert(dots <= 2);
-            if (dots == 2) {
-                // Turn "/x/y/../z" into "/x/z".
-                buf_next -= 4;  // "/../"
-                assert(*buf_next == SEP);
-                // We cap it off at the root, so "/../spam" becomes "/spam".
-                if (buf_next == buf_start) {
-                    buf_next++;
-                }
-                else {
-                    // Move to the previous SEP in the buffer.
-                    while (*(buf_next - 1) != SEP) {
-                        assert(buf_next != buf_start);
-                        buf_next--;
-                    }
-                }
-            }
-            else if (dots == 1) {
-                // Turn "/./" into "/".
-                buf_next -= 2;  // "./"
-                assert(*(buf_next - 1) == SEP);
-            }
-            else if (dots == 0) {
-                // Turn "//" into "/".
-                buf_next--;
-                assert(*(buf_next - 1) == SEP);
-                if (check_leading) {
-                    if (buf_next - 1 == buf && *(remainder + 1) != SEP) {
-                        // Leave a leading "//" alone, unless "///...".
-                        buf_next++;
-                        buf_start++;
-                    }
-                    check_leading = 0;
-                }
-            }
-            dots = 0;
+#define IS_END(x) (pEnd ? (x) == pEnd : !*(x))
+#ifdef ALTSEP
+#define IS_SEP(x) (*(x) == SEP || *(x) == ALTSEP)
+#else
+#define IS_SEP(x) (*(x) == SEP)
+#endif
+#define SEP_OR_END(x) (IS_SEP(x) || IS_END(x))
+
+    // Skip leading '.\'
+    if (p1[0] == L'.' && IS_SEP(&p1[1])) {
+        path = &path[2];
+        while (IS_SEP(path) && !IS_END(path)) {
+            path++;
         }
-        else {
-            check_leading = 0;
-            if (dots >= 0) {
-                if (c == L'.' && dots < 2) {
-                    dots++;
-                }
-                else {
-                    dots = -1;
-                }
+        p1 = p2 = minP2 = path;
+        lastC = SEP;
+    }
+#ifdef MS_WINDOWS
+    // Skip past drive segment and update minP2
+    else if (p1[0] && p1[1] == L':') {
+        *p2++ = *p1++;
+        *p2++ = *p1++;
+        minP2 = p2;
+        lastC = L':';
+    }
+    // Skip past all \\-prefixed paths, including \\?\, \\.\,
+    // and network paths, including the first segment.
+    else if (IS_SEP(&p1[0]) && IS_SEP(&p1[1])) {
+        int sepCount = 2;
+        *p2++ = SEP;
+        *p2++ = SEP;
+        p1 += 2;
+        for (; !IS_END(p1) && sepCount; ++p1) {
+            if (IS_SEP(p1)) {
+                --sepCount;
+                *p2++ = lastC = SEP;
+            } else {
+                *p2++ = lastC = *p1;
             }
         }
+        minP2 = p2;
     }
-    if (dots >= 0) {
-        // Strip any trailing dots and trailing slash.
-        buf_next -= dots + 1;  // "/" or "/." or "/.."
-        assert(*buf_next == SEP);
-        if (buf_next == buf_start) {
-            // Leave the leading slash for root.
-            buf_next++;
+#else
+    // Skip past two leading SEPs
+    else if (IS_SEP(&p1[0]) && IS_SEP(&p1[1]) && !IS_SEP(&p1[2])) {
+        *p2++ = *p1++;
+        *p2++ = *p1++;
+        minP2 = p2;
+        lastC = SEP;
+    }
+#endif /* MS_WINDOWS */
+
+    /* if pEnd is specified, check that. Else, check for null terminator */
+    for (; !IS_END(p1); ++p1) {
+        wchar_t c = *p1;
+#ifdef ALTSEP
+        if (c == ALTSEP) {
+            c = SEP;
         }
-        else {
-            if (dots == 2) {
-                // Move to the previous SEP in the buffer.
-                do {
-                    assert(buf_next != buf_start);
-                    buf_next--;
-                } while (*(buf_next) != SEP);
+#endif
+        if (lastC == SEP) {
+            if (c == L'.') {
+                int sep_at_1 = SEP_OR_END(&p1[1]);
+                int sep_at_2 = !sep_at_1 && SEP_OR_END(&p1[2]);
+                if (sep_at_2 && p1[1] == L'.') {
+                    wchar_t *p3 = p2;
+                    while (p3 != minP2 && *--p3 == SEP) { }
+                    while (p3 != minP2 && *(p3 - 1) != SEP) { --p3; }
+                    if (p3[0] == L'.' && p3[1] == L'.' && IS_SEP(&p3[2])) {
+                        // Previous segment is also ../, so append instead
+                        *p2++ = L'.';
+                        *p2++ = L'.';
+                        lastC = L'.';
+                    } else if (p3[0] == SEP) {
+                        // Absolute path, so absorb segment
+                        p2 = p3 + 1;
+                    } else {
+                        p2 = p3;
+                    }
+                    p1 += 1;
+                } else if (sep_at_1) {
+                } else {
+                    *p2++ = lastC = c;
+                }
+            } else if (c == SEP) {
+            } else {
+                *p2++ = lastC = c;
             }
+        } else {
+            *p2++ = lastC = c;
+        } 
+    }
+    *p2 = L'\0';
+    if (p2 != minP2) {
+        while (--p2 != minP2 && *p2 == SEP) {
+            *p2 = L'\0';
         }
     }
-    *buf_next = L'\0';
-    return 0;
+#undef SEP_OR_END
+#undef IS_SEP
+#undef IS_END
+    return path;
 }
 
 
diff --git a/Python/initconfig.c b/Python/initconfig.c
index 53b624f..47ebc64 100644
--- a/Python/initconfig.c
+++ b/Python/initconfig.c
@@ -22,11 +22,6 @@
 #  endif
 #endif
 
-#ifndef PLATLIBDIR
-#  error "PLATLIBDIR macro must be defined"
-#endif
-
-
 /* --- Command line options --------------------------------------- */
 
 /* Short usage message (with %s for argv0) */
@@ -632,7 +627,6 @@ config_check_consistency(const PyConfig *config)
     assert(config->parse_argv >= 0);
     assert(config->configure_c_stdio >= 0);
     assert(config->buffered_stdio >= 0);
-    assert(config->program_name != NULL);
     assert(_PyWideStringList_CheckConsistency(&config->orig_argv));
     assert(_PyWideStringList_CheckConsistency(&config->argv));
     /* sys.argv must be non-empty: empty argv is replaced with [''] */
@@ -641,7 +635,6 @@ config_check_consistency(const PyConfig *config)
     assert(_PyWideStringList_CheckConsistency(&config->warnoptions));
     assert(_PyWideStringList_CheckConsistency(&config->module_search_paths));
     assert(config->module_search_paths_set >= 0);
-    assert(config->platlibdir != NULL);
     assert(config->filesystem_encoding != NULL);
     assert(config->filesystem_errors != NULL);
     assert(config->stdio_encoding != NULL);
@@ -740,6 +733,7 @@ _PyConfig_InitCompatConfig(PyConfig *config)
     config->legacy_windows_stdio = -1;
 #endif
     config->use_frozen_modules = -1;
+    config->_is_python_build = 0;
     config->code_debug_ranges = 1;
 }
 
@@ -962,6 +956,7 @@ _PyConfig_Copy(PyConfig *config, const PyConfig *config2)
     COPY_ATTR(_isolated_interpreter);
     COPY_ATTR(use_frozen_modules);
     COPY_WSTRLIST(orig_argv);
+    COPY_ATTR(_is_python_build);
 
 #undef COPY_ATTR
 #undef COPY_WSTR_ATTR
@@ -1066,6 +1061,7 @@ _PyConfig_AsDict(const PyConfig *config)
     SET_ITEM_INT(_isolated_interpreter);
     SET_ITEM_WSTRLIST(orig_argv);
     SET_ITEM_INT(use_frozen_modules);
+    SET_ITEM_INT(_is_python_build);
 
     return dict;
 
@@ -1350,6 +1346,7 @@ _PyConfig_FromDict(PyConfig *config, PyObject *dict)
     GET_UINT(_init_main);
     GET_UINT(_isolated_interpreter);
     GET_UINT(use_frozen_modules);
+    GET_UINT(_is_python_build);
 
 #undef CHECK_VALUE
 #undef GET_UINT
@@ -1489,117 +1486,6 @@ config_set_global_vars(const PyConfig *config)
 }
 
 
-/* Get the program name: use PYTHONEXECUTABLE and __PYVENV_LAUNCHER__
-   environment variables on macOS if available. */
-static PyStatus
-config_init_program_name(PyConfig *config)
-{
-    PyStatus status;
-
-    /* If Py_SetProgramName() was called, use its value */
-    const wchar_t *program_name = _Py_path_config.program_name;
-    if (program_name != NULL) {
-        config->program_name = _PyMem_RawWcsdup(program_name);
-        if (config->program_name == NULL) {
-            return _PyStatus_NO_MEMORY();
-        }
-        return _PyStatus_OK();
-    }
-
-#ifdef __APPLE__
-    /* On MacOS X, when the Python interpreter is embedded in an
-       application bundle, it gets executed by a bootstrapping script
-       that does os.execve() with an argv[0] that's different from the
-       actual Python executable. This is needed to keep the Finder happy,
-       or rather, to work around Apple's overly strict requirements of
-       the process name. However, we still need a usable sys.executable,
-       so the actual executable path is passed in an environment variable.
-       See Lib/plat-mac/bundlebuilder.py for details about the bootstrap
-       script. */
-    const char *p = config_get_env(config, "PYTHONEXECUTABLE");
-    if (p != NULL) {
-        status = CONFIG_SET_BYTES_STR(config, &config->program_name, p,
-                                      "PYTHONEXECUTABLE environment variable");
-        if (_PyStatus_EXCEPTION(status)) {
-            return status;
-        }
-        return _PyStatus_OK();
-    }
-#ifdef WITH_NEXT_FRAMEWORK
-    else {
-        const char* pyvenv_launcher = getenv("__PYVENV_LAUNCHER__");
-        if (pyvenv_launcher && *pyvenv_launcher) {
-            /* Used by Mac/Tools/pythonw.c to forward
-             * the argv0 of the stub executable
-             */
-            status = CONFIG_SET_BYTES_STR(config,
-                                          &config->program_name,
-                                          pyvenv_launcher,
-                                          "__PYVENV_LAUNCHER__ environment variable");
-            if (_PyStatus_EXCEPTION(status)) {
-                return status;
-            }
-
-            /*
-             * This environment variable is used to communicate between
-             * the stub launcher and the real interpreter and isn't needed
-             * beyond this point.
-             *
-             * Clean up to avoid problems when launching other programs
-             * later on.
-             */
-            (void)unsetenv("__PYVENV_LAUNCHER__");
-
-            return _PyStatus_OK();
-        }
-    }
-#endif   /* WITH_NEXT_FRAMEWORK */
-#endif   /* __APPLE__ */
-
-    /* Use argv[0] if available and non-empty */
-    const PyWideStringList *argv = &config->argv;
-    if (argv->length >= 1 && argv->items[0][0] != L'\0') {
-        config->program_name = _PyMem_RawWcsdup(argv->items[0]);
-        if (config->program_name == NULL) {
-            return _PyStatus_NO_MEMORY();
-        }
-        return _PyStatus_OK();
-    }
-
-    /* Last fall back: hardcoded name */
-#ifdef MS_WINDOWS
-    const wchar_t *default_program_name = L"python";
-#else
-    const wchar_t *default_program_name = L"python3";
-#endif
-    status = PyConfig_SetString(config, &config->program_name,
-                                default_program_name);
-    if (_PyStatus_EXCEPTION(status)) {
-        return status;
-    }
-    return _PyStatus_OK();
-}
-
-static PyStatus
-config_init_executable(PyConfig *config)
-{
-    assert(config->executable == NULL);
-
-    /* If Py_SetProgramFullPath() was called, use its value */
-    const wchar_t *program_full_path = _Py_path_config.program_full_path;
-    if (program_full_path != NULL) {
-        PyStatus status = PyConfig_SetString(config,
-                                             &config->executable,
-                                             program_full_path);
-        if (_PyStatus_EXCEPTION(status)) {
-            return status;
-        }
-        return _PyStatus_OK();
-    }
-    return _PyStatus_OK();
-}
-
-
 static const wchar_t*
 config_get_xoption(const PyConfig *config, wchar_t *name)
 {
@@ -1619,25 +1505,6 @@ config_get_xoption_value(const PyConfig *config, wchar_t *name)
 
 
 static PyStatus
-config_init_home(PyConfig *config)
-{
-    assert(config->home == NULL);
-
-    /* If Py_SetPythonHome() was called, use its value */
-    wchar_t *home = _Py_path_config.home;
-    if (home) {
-        PyStatus status = PyConfig_SetString(config, &config->home, home);
-        if (_PyStatus_EXCEPTION(status)) {
-            return status;
-        }
-        return _PyStatus_OK();
-    }
-
-    return CONFIG_GET_ENV_DUP(config, &config->home,
-                              L"PYTHONHOME", "PYTHONHOME");
-}
-
-static PyStatus
 config_init_hash_seed(PyConfig *config)
 {
     const char *seed_text = config_get_env(config, "PYTHONHASHSEED");
@@ -2092,44 +1959,6 @@ config_init_fs_encoding(PyConfig *config, const PyPreConfig *preconfig)
 }
 
 
-/* Determine if the current build is a "development" build (e.g. running
-   out of the source tree) or not.
-
-   A return value of -1 indicates that we do not know.
-  */
-static int
-is_dev_env(PyConfig *config)
-{
-    // This should only ever get called early in runtime initialization,
-    // before the global path config is written.  Otherwise we would
-    // use Py_GetProgramFullPath() and _Py_GetStdlibDir().
-    assert(config != NULL);
-
-    const wchar_t *executable = config->executable;
-    const wchar_t *stdlib = config->stdlib_dir;
-    if (executable == NULL || *executable == L'\0' ||
-            stdlib == NULL || *stdlib == L'\0') {
-        // _PyPathConfig_Calculate() hasn't run yet.
-        return -1;
-    }
-    size_t len = _Py_find_basename(executable);
-    if (wcscmp(executable + len, L"python") != 0 &&
-            wcscmp(executable + len, L"python.exe") != 0) {
-        return 0;
-    }
-    /* If dirname() is the same for both then it is a dev build. */
-    if (len != _Py_find_basename(stdlib)) {
-        return 0;
-    }
-    // We do not bother normalizing the two filenames first since
-    // for config_init_import() is does the right thing as-is.
-    if (wcsncmp(stdlib, executable, len) != 0) {
-        return 0;
-    }
-    return 1;
-}
-
-
 static PyStatus
 config_init_import(PyConfig *config, int compute_path_config)
 {
@@ -2144,10 +1973,7 @@ config_init_import(PyConfig *config, int compute_path_config)
     if (config->use_frozen_modules < 0) {
         const wchar_t *value = config_get_xoption_value(config, L"frozen_modules");
         if (value == NULL) {
-            int isdev = is_dev_env(config);
-            if (isdev >= 0) {
-                config->use_frozen_modules = !isdev;
-            }
+            config->use_frozen_modules = !config->_is_python_build;
         }
         else if (wcscmp(value, L"on") == 0) {
             config->use_frozen_modules = 1;
@@ -2246,28 +2072,6 @@ config_read(PyConfig *config, int compute_path_config)
         return status;
     }
 
-    if (config->home == NULL) {
-        status = config_init_home(config);
-        if (_PyStatus_EXCEPTION(status)) {
-            return status;
-        }
-    }
-
-    if (config->executable == NULL) {
-        status = config_init_executable(config);
-        if (_PyStatus_EXCEPTION(status)) {
-            return status;
-        }
-    }
-
-    if(config->platlibdir == NULL) {
-        status = CONFIG_SET_BYTES_STR(config, &config->platlibdir, PLATLIBDIR,
-                                      "PLATLIBDIR macro");
-        if (_PyStatus_EXCEPTION(status)) {
-            return status;
-        }
-    }
-
     if (config->_install_importlib) {
         status = config_init_import(config, compute_path_config);
         if (_PyStatus_EXCEPTION(status)) {
@@ -2890,13 +2694,6 @@ config_read_cmdline(PyConfig *config)
         config->parse_argv = 1;
     }
 
-    if (config->program_name == NULL) {
-        status = config_init_program_name(config);
-        if (_PyStatus_EXCEPTION(status)) {
-            return status;
-        }
-    }
-
     if (config->parse_argv == 1) {
         Py_ssize_t opt_index;
         status = config_parse_cmdline(config, &cmdline_warnoptions, &opt_index);
@@ -3076,7 +2873,7 @@ done:
 PyStatus
 PyConfig_Read(PyConfig *config)
 {
-    return _PyConfig_Read(config, 1);
+    return _PyConfig_Read(config, 0);
 }
 
 
@@ -3124,16 +2921,6 @@ _Py_GetConfigsAsDict(void)
     }
     Py_CLEAR(dict);
 
-    /* path config */
-    dict = _PyPathConfig_AsDict();
-    if (dict == NULL) {
-        goto error;
-    }
-    if (PyDict_SetItemString(result, "path_config", dict) < 0) {
-        goto error;
-    }
-    Py_CLEAR(dict);
-
     return result;
 
 error:
@@ -3199,6 +2986,7 @@ _Py_DumpPathConfig(PyThreadState *tstate)
     PySys_WriteStderr("  environment = %i\n", config->use_environment);
     PySys_WriteStderr("  user site = %i\n", config->user_site_directory);
     PySys_WriteStderr("  import site = %i\n", config->site_import);
+    PySys_WriteStderr("  is in build tree = %i\n", config->_is_python_build);
     DUMP_CONFIG("stdlib dir", stdlib_dir);
 #undef DUMP_CONFIG
 
diff --git a/Python/pathconfig.c b/Python/pathconfig.c
index ad22222..4271928 100644
--- a/Python/pathconfig.c
+++ b/Python/pathconfig.c
@@ -1,6 +1,7 @@
 /* Path configuration like module_search_path (sys.path) */
 
 #include "Python.h"
+#include "marshal.h"              // PyMarshal_ReadObjectFromString
 #include "osdefs.h"               // DELIM
 #include "pycore_initconfig.h"
 #include "pycore_fileutils.h"
@@ -9,6 +10,8 @@
 #include <wchar.h>
 #ifdef MS_WINDOWS
 #  include <windows.h>            // GetFullPathNameW(), MAX_PATH
+#  include <pathcch.h>
+#  include <shlwapi.h>
 #endif
 
 #ifdef __cplusplus
@@ -16,462 +19,170 @@ extern "C" {
 #endif
 
 
+/* External interface */
+
+/* Stored values set by C API functions */
+typedef struct _PyPathConfig {
+    /* Full path to the Python program */
+    wchar_t *program_full_path;
+    wchar_t *prefix;
+    wchar_t *exec_prefix;
+    wchar_t *stdlib_dir;
+    /* Set by Py_SetPath */
+    wchar_t *module_search_path;
+    /* Set by _PyPathConfig_UpdateGlobal */
+    wchar_t *calculated_module_search_path;
+    /* Python program name */
+    wchar_t *program_name;
+    /* Set by Py_SetPythonHome() or PYTHONHOME environment variable */
+    wchar_t *home;
+} _PyPathConfig;
+
+#  define _PyPathConfig_INIT \
+      {.module_search_path = NULL}
+
+
 _PyPathConfig _Py_path_config = _PyPathConfig_INIT;
 
 
-static int
-copy_wstr(wchar_t **dst, const wchar_t *src)
+const wchar_t *
+_PyPathConfig_GetGlobalModuleSearchPath(void)
 {
-    assert(*dst == NULL);
-    if (src != NULL) {
-        *dst = _PyMem_RawWcsdup(src);
-        if (*dst == NULL) {
-            return -1;
-        }
-    }
-    else {
-        *dst = NULL;
-    }
-    return 0;
+    return _Py_path_config.module_search_path;
 }
 
 
-static void
-pathconfig_clear(_PyPathConfig *config)
+void
+_PyPathConfig_ClearGlobal(void)
 {
-    /* _PyMem_SetDefaultAllocator() is needed to get a known memory allocator,
-       since Py_SetPath(), Py_SetPythonHome() and Py_SetProgramName() can be
-       called before Py_Initialize() which can changes the memory allocator. */
     PyMemAllocatorEx old_alloc;
     _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 
 #define CLEAR(ATTR) \
     do { \
-        PyMem_RawFree(ATTR); \
-        ATTR = NULL; \
+        PyMem_RawFree(_Py_path_config.ATTR); \
+        _Py_path_config.ATTR = NULL; \
     } while (0)
 
-    CLEAR(config->program_full_path);
-    CLEAR(config->prefix);
-    CLEAR(config->exec_prefix);
-    CLEAR(config->stdlib_dir);
-    CLEAR(config->module_search_path);
-    CLEAR(config->program_name);
-    CLEAR(config->home);
-#ifdef MS_WINDOWS
-    CLEAR(config->base_executable);
-#endif
+    CLEAR(program_full_path);
+    CLEAR(prefix);
+    CLEAR(exec_prefix);
+    CLEAR(stdlib_dir);
+    CLEAR(module_search_path);
+    CLEAR(calculated_module_search_path);
+    CLEAR(program_name);
+    CLEAR(home);
 
 #undef CLEAR
 
     PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 }
 
-
-static PyStatus
-pathconfig_copy(_PyPathConfig *config, const _PyPathConfig *config2)
+PyStatus
+_PyPathConfig_ReadGlobal(PyConfig *config)
 {
-    pathconfig_clear(config);
+    PyStatus status = _PyStatus_OK();
 
-#define COPY_ATTR(ATTR) \
+#define COPY(ATTR) \
     do { \
-        if (copy_wstr(&config->ATTR, config2->ATTR) < 0) { \
-            return _PyStatus_NO_MEMORY(); \
+        if (_Py_path_config.ATTR && !config->ATTR) { \
+            status = PyConfig_SetString(config, &config->ATTR, _Py_path_config.ATTR); \
+            if (_PyStatus_EXCEPTION(status)) goto done; \
         } \
     } while (0)
 
-    COPY_ATTR(program_full_path);
-    COPY_ATTR(prefix);
-    COPY_ATTR(exec_prefix);
-    COPY_ATTR(module_search_path);
-    COPY_ATTR(stdlib_dir);
-    COPY_ATTR(program_name);
-    COPY_ATTR(home);
-#ifdef MS_WINDOWS
-    config->isolated = config2->isolated;
-    config->site_import = config2->site_import;
-    COPY_ATTR(base_executable);
-#endif
-
-#undef COPY_ATTR
-
-    return _PyStatus_OK();
-}
-
-
-void
-_PyPathConfig_ClearGlobal(void)
-{
-    PyMemAllocatorEx old_alloc;
-    _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
-
-    pathconfig_clear(&_Py_path_config);
-
-    PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
-}
-
-
-static wchar_t*
-_PyWideStringList_Join(const PyWideStringList *list, wchar_t sep)
-{
-    size_t len = 1;   /* NUL terminator */
-    for (Py_ssize_t i=0; i < list->length; i++) {
-        if (i != 0) {
-            len++;
-        }
-        len += wcslen(list->items[i]);
-    }
-
-    wchar_t *text = PyMem_RawMalloc(len * sizeof(wchar_t));
-    if (text == NULL) {
-        return NULL;
-    }
-    wchar_t *str = text;
-    for (Py_ssize_t i=0; i < list->length; i++) {
-        wchar_t *path = list->items[i];
-        if (i != 0) {
-            *str++ = sep;
-        }
-        len = wcslen(path);
-        memcpy(str, path, len * sizeof(wchar_t));
-        str += len;
-    }
-    *str = L'\0';
-
-    return text;
-}
-
-
-static PyStatus
-pathconfig_set_from_config(_PyPathConfig *pathconfig, const PyConfig *config)
-{
-    PyStatus status;
-    PyMemAllocatorEx old_alloc;
-    _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
-
-    if (config->module_search_paths_set) {
-        PyMem_RawFree(pathconfig->module_search_path);
-        pathconfig->module_search_path = _PyWideStringList_Join(&config->module_search_paths, DELIM);
-        if (pathconfig->module_search_path == NULL) {
-            goto no_memory;
-        }
-    }
-
-#define COPY_CONFIG(PATH_ATTR, CONFIG_ATTR) \
-        if (config->CONFIG_ATTR) { \
-            PyMem_RawFree(pathconfig->PATH_ATTR); \
-            pathconfig->PATH_ATTR = NULL; \
-            if (copy_wstr(&pathconfig->PATH_ATTR, config->CONFIG_ATTR) < 0) { \
-                goto no_memory; \
-            } \
-        }
-
-    COPY_CONFIG(program_full_path, executable);
-    COPY_CONFIG(prefix, prefix);
-    COPY_CONFIG(exec_prefix, exec_prefix);
-    COPY_CONFIG(stdlib_dir, stdlib_dir);
-    COPY_CONFIG(program_name, program_name);
-    COPY_CONFIG(home, home);
-#ifdef MS_WINDOWS
-    COPY_CONFIG(base_executable, base_executable);
-#endif
-
-#undef COPY_CONFIG
-
-    status = _PyStatus_OK();
-    goto done;
+#define COPY2(ATTR, SRCATTR) \
+    do { \
+        if (_Py_path_config.SRCATTR && !config->ATTR) { \
+            status = PyConfig_SetString(config, &config->ATTR, _Py_path_config.SRCATTR); \
+            if (_PyStatus_EXCEPTION(status)) goto done; \
+        } \
+    } while (0)
 
-no_memory:
-    status = _PyStatus_NO_MEMORY();
+    COPY(prefix);
+    COPY(exec_prefix);
+    COPY(stdlib_dir);
+    COPY(program_name);
+    COPY(home);
+    COPY2(executable, program_full_path);
+    // module_search_path must be initialised - not read
+#undef COPY
+#undef COPY2
 
 done:
-    PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
     return status;
 }
 
-PyObject *
-_PyPathConfig_AsDict(void)
-{
-    PyObject *dict = PyDict_New();
-    if (dict == NULL) {
-        return NULL;
-    }
-
-#define SET_ITEM(KEY, EXPR) \
-        do { \
-            PyObject *obj = (EXPR); \
-            if (obj == NULL) { \
-                goto fail; \
-            } \
-            int res = PyDict_SetItemString(dict, KEY, obj); \
-            Py_DECREF(obj); \
-            if (res < 0) { \
-                goto fail; \
-            } \
-        } while (0)
-#define SET_ITEM_STR(KEY) \
-        SET_ITEM(#KEY, \
-            (_Py_path_config.KEY \
-             ? PyUnicode_FromWideChar(_Py_path_config.KEY, -1) \
-             : (Py_INCREF(Py_None), Py_None)))
-#define SET_ITEM_INT(KEY) \
-        SET_ITEM(#KEY, PyLong_FromLong(_Py_path_config.KEY))
-
-    SET_ITEM_STR(program_full_path);
-    SET_ITEM_STR(prefix);
-    SET_ITEM_STR(exec_prefix);
-    SET_ITEM_STR(module_search_path);
-    SET_ITEM_STR(stdlib_dir);
-    SET_ITEM_STR(program_name);
-    SET_ITEM_STR(home);
-#ifdef MS_WINDOWS
-    SET_ITEM_INT(isolated);
-    SET_ITEM_INT(site_import);
-    SET_ITEM_STR(base_executable);
-
-    {
-        wchar_t py3path[MAX_PATH];
-        HMODULE hPython3 = GetModuleHandleW(PY3_DLLNAME);
-        PyObject *obj;
-        if (hPython3
-            && GetModuleFileNameW(hPython3, py3path, Py_ARRAY_LENGTH(py3path)))
-        {
-            obj = PyUnicode_FromWideChar(py3path, -1);
-            if (obj == NULL) {
-                goto fail;
-            }
-        }
-        else {
-            obj = Py_None;
-            Py_INCREF(obj);
-        }
-        if (PyDict_SetItemString(dict, "python3_dll", obj) < 0) {
-            Py_DECREF(obj);
-            goto fail;
-        }
-        Py_DECREF(obj);
-    }
-#endif
-
-#undef SET_ITEM
-#undef SET_ITEM_STR
-#undef SET_ITEM_INT
-
-    return dict;
-
-fail:
-    Py_DECREF(dict);
-    return NULL;
-}
-
-
 PyStatus
-_PyConfig_WritePathConfig(const PyConfig *config)
+_PyPathConfig_UpdateGlobal(const PyConfig *config)
 {
-    return pathconfig_set_from_config(&_Py_path_config, config);
-}
-
-
-static PyStatus
-config_init_module_search_paths(PyConfig *config, _PyPathConfig *pathconfig)
-{
-    assert(!config->module_search_paths_set);
-
-    _PyWideStringList_Clear(&config->module_search_paths);
-
-    const wchar_t *sys_path = pathconfig->module_search_path;
-    const wchar_t delim = DELIM;
-    while (1) {
-        const wchar_t *p = wcschr(sys_path, delim);
-        if (p == NULL) {
-            p = sys_path + wcslen(sys_path); /* End of string */
-        }
-
-        size_t path_len = (p - sys_path);
-        wchar_t *path = PyMem_RawMalloc((path_len + 1) * sizeof(wchar_t));
-        if (path == NULL) {
-            return _PyStatus_NO_MEMORY();
-        }
-        memcpy(path, sys_path, path_len * sizeof(wchar_t));
-        path[path_len] = L'\0';
-
-        PyStatus status = PyWideStringList_Append(&config->module_search_paths, path);
-        PyMem_RawFree(path);
-        if (_PyStatus_EXCEPTION(status)) {
-            return status;
-        }
-
-        if (*p == '\0') {
-            break;
-        }
-        sys_path = p + 1;
-    }
-    config->module_search_paths_set = 1;
-    return _PyStatus_OK();
-}
-
-
-/* Calculate the path configuration:
-
-   - exec_prefix
-   - module_search_path
-   - stdlib_dir
-   - prefix
-   - program_full_path
-
-   On Windows, more fields are calculated:
-
-   - base_executable
-   - isolated
-   - site_import
-
-   On other platforms, isolated and site_import are left unchanged, and
-   _PyConfig_InitPathConfig() copies executable to base_executable (if it's not
-   set).
-
-   Priority, highest to lowest:
-
-   - PyConfig
-   - _Py_path_config: set by Py_SetPath(), Py_SetPythonHome()
-     and Py_SetProgramName()
-   - _PyPathConfig_Calculate()
-*/
-static PyStatus
-pathconfig_init(_PyPathConfig *pathconfig, const PyConfig *config,
-                int compute_path_config)
-{
-    PyStatus status;
-
     PyMemAllocatorEx old_alloc;
     _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 
-    status = pathconfig_copy(pathconfig, &_Py_path_config);
-    if (_PyStatus_EXCEPTION(status)) {
-        goto done;
-    }
-
-    status = pathconfig_set_from_config(pathconfig, config);
-    if (_PyStatus_EXCEPTION(status)) {
-        goto done;
-    }
-
-    if (compute_path_config) {
-        status = _PyPathConfig_Calculate(pathconfig, config);
-    }
-
-done:
-    PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
-    return status;
-}
-
-
-static PyStatus
-config_init_pathconfig(PyConfig *config, int compute_path_config)
-{
-    _PyPathConfig pathconfig = _PyPathConfig_INIT;
-    PyStatus status;
-
-    status = pathconfig_init(&pathconfig, config, compute_path_config);
-    if (_PyStatus_EXCEPTION(status)) {
-        goto done;
-    }
-
-    if (!config->module_search_paths_set
-        && pathconfig.module_search_path != NULL)
-    {
-        status = config_init_module_search_paths(config, &pathconfig);
-        if (_PyStatus_EXCEPTION(status)) {
-            goto done;
-        }
-    }
-
-#define COPY_ATTR(PATH_ATTR, CONFIG_ATTR) \
-        if (config->CONFIG_ATTR == NULL && pathconfig.PATH_ATTR != NULL) { \
-            if (copy_wstr(&config->CONFIG_ATTR, pathconfig.PATH_ATTR) < 0) { \
-                goto no_memory; \
-            } \
-        }
-
-#ifdef MS_WINDOWS
-    if (config->executable != NULL && config->base_executable == NULL) {
-        /* If executable is set explicitly in the configuration,
-           ignore calculated base_executable: _PyConfig_InitPathConfig()
-           will copy executable to base_executable */
-    }
-    else {
-        COPY_ATTR(base_executable, base_executable);
-    }
-#endif
-
-    COPY_ATTR(program_full_path, executable);
-    COPY_ATTR(prefix, prefix);
-    COPY_ATTR(exec_prefix, exec_prefix);
-    COPY_ATTR(stdlib_dir, stdlib_dir);
-
-#undef COPY_ATTR
-
-#ifdef MS_WINDOWS
-    /* If a ._pth file is found: isolated and site_import are overridden */
-    if (pathconfig.isolated != -1) {
-        config->isolated = pathconfig.isolated;
-    }
-    if (pathconfig.site_import != -1) {
-        config->site_import = pathconfig.site_import;
-    }
-#endif
-
-    status = _PyStatus_OK();
-    goto done;
-
-no_memory:
-    status = _PyStatus_NO_MEMORY();
+#define COPY(ATTR) \
+    do { \
+        if (config->ATTR) { \
+            PyMem_RawFree(_Py_path_config.ATTR); \
+            _Py_path_config.ATTR = _PyMem_RawWcsdup(config->ATTR); \
+            if (!_Py_path_config.ATTR) goto error; \
+        } \
+    } while (0)
 
-done:
-    pathconfig_clear(&pathconfig);
-    return status;
-}
+#define COPY2(ATTR, SRCATTR) \
+    do { \
+        if (config->SRCATTR) { \
+            PyMem_RawFree(_Py_path_config.ATTR); \
+            _Py_path_config.ATTR = _PyMem_RawWcsdup(config->SRCATTR); \
+            if (!_Py_path_config.ATTR) goto error; \
+        } \
+    } while (0)
 
+    COPY(prefix);
+    COPY(exec_prefix);
+    COPY(stdlib_dir);
+    COPY(program_name);
+    COPY(home);
+    COPY2(program_full_path, executable);
+#undef COPY
+#undef COPY2
 
-PyStatus
-_PyConfig_InitPathConfig(PyConfig *config, int compute_path_config)
-{
-    /* Do we need to calculate the path? */
-    if (!config->module_search_paths_set
-        || config->executable == NULL
-        || config->prefix == NULL
-        || config->exec_prefix == NULL)
-    {
-        PyStatus status = config_init_pathconfig(config, compute_path_config);
-        if (_PyStatus_EXCEPTION(status)) {
-            return status;
+    PyMem_RawFree(_Py_path_config.module_search_path);
+    _Py_path_config.module_search_path = NULL;
+    PyMem_RawFree(_Py_path_config.calculated_module_search_path);
+    _Py_path_config.calculated_module_search_path = NULL;
+
+    do {
+        size_t cch = 1;
+        for (Py_ssize_t i = 0; i < config->module_search_paths.length; ++i) {
+            cch += 1 + wcslen(config->module_search_paths.items[i]);
         }
-    }
 
-    if (config->base_prefix == NULL && config->prefix != NULL) {
-        if (copy_wstr(&config->base_prefix, config->prefix) < 0) {
-            return _PyStatus_NO_MEMORY();
+        wchar_t *path = (wchar_t*)PyMem_RawMalloc(sizeof(wchar_t) * cch);
+        if (!path) {
+            goto error;
         }
-    }
-
-    if (config->base_exec_prefix == NULL && config->exec_prefix != NULL) {
-        if (copy_wstr(&config->base_exec_prefix,
-                      config->exec_prefix) < 0) {
-            return _PyStatus_NO_MEMORY();
+        wchar_t *p = path;
+        for (Py_ssize_t i = 0; i < config->module_search_paths.length; ++i) {
+            wcscpy(p, config->module_search_paths.items[i]);
+            p = wcschr(p, L'\0');
+            *p++ = DELIM;
+            *p = L'\0';
         }
-    }
 
-    if (config->base_executable == NULL && config->executable != NULL) {
-        if (copy_wstr(&config->base_executable,
-                      config->executable) < 0) {
-            return _PyStatus_NO_MEMORY();
-        }
-    }
+        do {
+            *p = L'\0';
+        } while (p != path && *--p == DELIM);
+        _Py_path_config.calculated_module_search_path = path;
+    } while (0);
 
+    PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
     return _PyStatus_OK();
-}
 
+error:
+    PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
+    return _PyStatus_NO_MEMORY();
+}
 
-/* External interface */
 
 static void _Py_NO_RETURN
 path_out_of_memory(const char *func)
@@ -483,7 +194,7 @@ void
 Py_SetPath(const wchar_t *path)
 {
     if (path == NULL) {
-        pathconfig_clear(&_Py_path_config);
+        _PyPathConfig_ClearGlobal();
         return;
     }
 
@@ -494,6 +205,7 @@ Py_SetPath(const wchar_t *path)
     PyMem_RawFree(_Py_path_config.exec_prefix);
     PyMem_RawFree(_Py_path_config.stdlib_dir);
     PyMem_RawFree(_Py_path_config.module_search_path);
+    PyMem_RawFree(_Py_path_config.calculated_module_search_path);
 
     _Py_path_config.prefix = _PyMem_RawWcsdup(L"");
     _Py_path_config.exec_prefix = _PyMem_RawWcsdup(L"");
@@ -505,6 +217,7 @@ Py_SetPath(const wchar_t *path)
         _Py_path_config.stdlib_dir = _PyMem_RawWcsdup(L"");
     }
     _Py_path_config.module_search_path = _PyMem_RawWcsdup(path);
+    _Py_path_config.calculated_module_search_path = NULL;
 
     PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 
@@ -521,19 +234,19 @@ Py_SetPath(const wchar_t *path)
 void
 Py_SetPythonHome(const wchar_t *home)
 {
-    if (home == NULL) {
-        return;
-    }
+    int has_value = home && home[0];
 
     PyMemAllocatorEx old_alloc;
     _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 
     PyMem_RawFree(_Py_path_config.home);
-    _Py_path_config.home = _PyMem_RawWcsdup(home);
+    if (has_value) {
+        _Py_path_config.home = _PyMem_RawWcsdup(home);
+    }
 
     PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 
-    if (_Py_path_config.home == NULL) {
+    if (has_value && _Py_path_config.home == NULL) {
         path_out_of_memory(__func__);
     }
 }
@@ -542,19 +255,19 @@ Py_SetPythonHome(const wchar_t *home)
 void
 Py_SetProgramName(const wchar_t *program_name)
 {
-    if (program_name == NULL || program_name[0] == L'\0') {
-        return;
-    }
+    int has_value = program_name && program_name[0];
 
     PyMemAllocatorEx old_alloc;
     _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 
     PyMem_RawFree(_Py_path_config.program_name);
-    _Py_path_config.program_name = _PyMem_RawWcsdup(program_name);
+    if (has_value) {
+        _Py_path_config.program_name = _PyMem_RawWcsdup(program_name);
+    }
 
     PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 
-    if (_Py_path_config.program_name == NULL) {
+    if (has_value && _Py_path_config.program_name == NULL) {
         path_out_of_memory(__func__);
     }
 }
@@ -562,19 +275,19 @@ Py_SetProgramName(const wchar_t *program_name)
 void
 _Py_SetProgramFullPath(const wchar_t *program_full_path)
 {
-    if (program_full_path == NULL || program_full_path[0] == L'\0') {
-        return;
-    }
+    int has_value = program_full_path && program_full_path[0];
 
     PyMemAllocatorEx old_alloc;
     _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 
     PyMem_RawFree(_Py_path_config.program_full_path);
-    _Py_path_config.program_full_path = _PyMem_RawWcsdup(program_full_path);
+    if (has_value) {
+        _Py_path_config.program_full_path = _PyMem_RawWcsdup(program_full_path);
+    }
 
     PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 
-    if (_Py_path_config.program_full_path == NULL) {
+    if (has_value && _Py_path_config.program_full_path == NULL) {
         path_out_of_memory(__func__);
     }
 }
@@ -583,7 +296,12 @@ _Py_SetProgramFullPath(const wchar_t *program_full_path)
 wchar_t *
 Py_GetPath(void)
 {
-    return _Py_path_config.module_search_path;
+    /* If the user has provided a path, return that */
+    if (_Py_path_config.module_search_path) {
+        return _Py_path_config.module_search_path;
+    }
+    /* If we have already done calculations, return the calculated path */
+    return _Py_path_config.calculated_module_search_path;
 }
 
 
@@ -632,6 +350,8 @@ Py_GetProgramName(void)
     return _Py_path_config.program_name;
 }
 
+
+
 /* Compute module search path from argv[0] or the current working
    directory ("-m module" case) which will be prepended to sys.argv:
    sys.path[0].
@@ -772,73 +492,6 @@ _PyPathConfig_ComputeSysPath0(const PyWideStringList *argv, PyObject **path0_p)
 }
 
 
-#ifdef MS_WINDOWS
-#define WCSTOK wcstok_s
-#else
-#define WCSTOK wcstok
-#endif
-
-/* Search for a prefix value in an environment file (pyvenv.cfg).
-
-   - If found, copy it into *value_p: string which must be freed by
-     PyMem_RawFree().
-   - If not found, *value_p is set to NULL.
-*/
-PyStatus
-_Py_FindEnvConfigValue(FILE *env_file, const wchar_t *key,
-                       wchar_t **value_p)
-{
-    *value_p = NULL;
-
-    char buffer[MAXPATHLEN * 2 + 1];  /* allow extra for key, '=', etc. */
-    buffer[Py_ARRAY_LENGTH(buffer)-1] = '\0';
-
-    while (!feof(env_file)) {
-        char * p = fgets(buffer, Py_ARRAY_LENGTH(buffer) - 1, env_file);
-
-        if (p == NULL) {
-            break;
-        }
-
-        size_t n = strlen(p);
-        if (p[n - 1] != '\n') {
-            /* line has overflowed - bail */
-            break;
-        }
-        if (p[0] == '#') {
-            /* Comment - skip */
-            continue;
-        }
-
-        wchar_t *tmpbuffer = _Py_DecodeUTF8_surrogateescape(buffer, n, NULL);
-        if (tmpbuffer) {
-            wchar_t * state;
-            wchar_t * tok = WCSTOK(tmpbuffer, L" \t\r\n", &state);
-            if ((tok != NULL) && !wcscmp(tok, key)) {
-                tok = WCSTOK(NULL, L" \t", &state);
-                if ((tok != NULL) && !wcscmp(tok, L"=")) {
-                    tok = WCSTOK(NULL, L"\r\n", &state);
-                    if (tok != NULL) {
-                        *value_p = _PyMem_RawWcsdup(tok);
-                        PyMem_RawFree(tmpbuffer);
-
-                        if (*value_p == NULL) {
-                            return _PyStatus_NO_MEMORY();
-                        }
-
-                        /* found */
-                        return _PyStatus_OK();
-                    }
-                }
-            }
-            PyMem_RawFree(tmpbuffer);
-        }
-    }
-
-    /* not found */
-    return _PyStatus_OK();
-}
-
 #ifdef __cplusplus
 }
 #endif
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index c6b2a1e..84b76ea 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -459,7 +459,7 @@ interpreter_update_config(PyThreadState *tstate, int only_update_path_config)
     }
 
     if (_Py_IsMainInterpreter(tstate->interp)) {
-        PyStatus status = _PyConfig_WritePathConfig(config);
+        PyStatus status = _PyPathConfig_UpdateGlobal(config);
         if (_PyStatus_EXCEPTION(status)) {
             _PyErr_SetFromPyStatus(status);
             return -1;
@@ -488,7 +488,7 @@ _PyInterpreterState_SetConfig(const PyConfig *src_config)
         goto done;
     }
 
-    status = PyConfig_Read(&config);
+    status = _PyConfig_Read(&config, 1);
     if (_PyStatus_EXCEPTION(status)) {
         _PyErr_SetFromPyStatus(status);
         goto done;
@@ -549,7 +549,7 @@ pyinit_core_reconfigure(_PyRuntimeState *runtime,
     config = _PyInterpreterState_GetConfig(interp);
 
     if (config->_install_importlib) {
-        status = _PyConfig_WritePathConfig(config);
+        status = _PyPathConfig_UpdateGlobal(config);
         if (_PyStatus_EXCEPTION(status)) {
             return status;
         }