kushaldas’s pypackages cpython branch mashed in to Python 3.7 for *easier* testing

pypackages-3.7.patch

diff --git i/Include/pystate.h w/Include/pystate.h
index 29d7148..7446df7 100644
--- i/Include/pystate.h
+++ w/Include/pystate.h
@@ -62,6 +62,8 @@ typedef struct {
     wchar_t *home;          /* PYTHONHOME environment variable,
                                see also Py_SetPythonHome(). */
 
+    wchar_t *pypackages_path; /* For __pypackages__ directory */
+
     /* Path configuration outputs */
     int nmodule_search_path;        /* Number of sys.path paths,
                                        -1 means unset */
diff --git i/Modules/getpath.c w/Modules/getpath.c
index e6a3e8e..8363949 100644
--- i/Modules/getpath.c
+++ w/Modules/getpath.c
@@ -763,6 +763,10 @@ calculate_module_search_path(const _PyCoreConfig *core_config,
         bufsz += wcslen(core_config->module_search_path_env) + 1;
     }
 
+    if (core_config->pypackages_path != NULL) {
+        bufsz += wcslen(core_config->pypackages_path) + 1;
+    }
+
     wchar_t *defpath = calculate->pythonpath;
     size_t prefixsz = wcslen(prefix) + 1;
     while (1) {
@@ -799,6 +803,12 @@ calculate_module_search_path(const _PyCoreConfig *core_config,
         wcscat(buf, delimiter);
     }
 
+    /* Add __pypackages__ directory */
+    if (core_config->pypackages_path) {
+        wcscpy(buf, core_config->pypackages_path);
+        wcscat(buf, delimiter);
+    }
+
     /* Next is the default zip path */
     wcscat(buf, calculate->zip_path);
     wcscat(buf, delimiter);
diff --git i/Modules/main.c w/Modules/main.c
index 286ad41..ef6f29f 100644
--- i/Modules/main.c
+++ w/Modules/main.c
@@ -732,6 +732,53 @@ pymain_wstrlist_append(_PyMain *pymain, int *len, wchar_t ***list, const wchar_t
     return 0;
 }
 
+static wchar_t *
+py_dirname(const wchar_t *filename)
+{
+    wchar_t *dir = _PyMem_RawWcsdup(filename);
+    if (dir == NULL) {
+        return NULL;
+    }
+    size_t i = wcslen(dir);
+
+#ifdef ALTSEP
+    while (i > 0 && dir[i] != SEP && dir[i] != ALTSEP)
+        --i;
+#else
+    while (i > 0 && dir[i] != SEP)
+        --i;
+#endif
+    if (i == 0) {
+        dir[0] = L'.';
+        i++;
+    }
+    dir[i] = '\0';
+
+    char buffer[100];
+    PyOS_snprintf(buffer, sizeof(buffer), "%c__pypackages__%c%d.%d%clib", SEP, SEP, PY_MAJOR_VERSION, PY_MINOR_VERSION, SEP);
+    wchar_t *pybuffer = Py_DecodeLocale(buffer, NULL);
+    if (pybuffer == NULL) {
+        PyMem_RawFree(dir);
+        return NULL;
+    }
+    size_t buffer_len = wcslen(dir) + wcslen(pybuffer) + 1;
+
+    wchar_t *final_path = PyMem_RawMalloc(buffer_len * sizeof(wchar_t));
+    if (final_path == NULL) {
+        PyMem_RawFree(dir);
+        PyMem_RawFree(pybuffer);
+        return NULL;
+    }
+
+    wcscpy(final_path, dir);
+    wcscat(final_path, pybuffer);
+
+    PyMem_RawFree(dir);
+    PyMem_RawFree(pybuffer);
+
+
+    return final_path;
+}
 
 /* Parse the command line arguments
    Return 0 on success.
@@ -1911,6 +1958,24 @@ pymain_read_conf_impl(_PyMain *pymain, _Py_CommandLineDetails *cmdline)
         return -1;
     }
 
+    /* In case of script files */
+    if (pymain->filename != NULL) {
+        config->pypackages_path = py_dirname(pymain->filename);
+        if (config->pypackages_path == NULL) {
+            pymain->err = _Py_INIT_NO_MEMORY();
+            return -1;
+        }
+    } else {
+        /* For the rest of the cases. */
+        char buffer[10];
+        PyOS_snprintf(buffer, sizeof(buffer), ".%c.", SEP);
+        config->pypackages_path = py_dirname(Py_DecodeLocale(buffer, NULL));
+        if (config->pypackages_path == NULL) {
+            pymain->err = _Py_INIT_NO_MEMORY();
+            return -1;
+        }
+    }
+
     /* On Windows, _PyPathConfig_Init() modifies Py_IsolatedFlag and
        Py_NoSiteFlag variables if a "._pth" file is found. */
     int init_isolated = Py_IsolatedFlag;
@@ -2239,6 +2304,7 @@ _PyCoreConfig_Clear(_PyCoreConfig *config)
 
     CLEAR(config->module_search_path_env);
     CLEAR(config->home);
+    CLEAR(config->pypackages_path);
     CLEAR(config->program_name);
     CLEAR(config->program);
 
@@ -2303,6 +2369,7 @@ _PyCoreConfig_Copy(_PyCoreConfig *config, const _PyCoreConfig *config2)
 
     COPY_STR_ATTR(module_search_path_env);
     COPY_STR_ATTR(home);
+    COPY_STR_ATTR(pypackages_path);
     COPY_STR_ATTR(program_name);
     COPY_STR_ATTR(program);
 
diff --git i/PC/getpathp.c w/PC/getpathp.c
index 9382843..aceb6af 100644
--- i/PC/getpathp.c
+++ w/PC/getpathp.c
@@ -800,6 +800,9 @@ calculate_module_search_path(const _PyCoreConfig *core_config,
     if (calculate->user_path) {
         bufsz += wcslen(calculate->user_path) + 1;
     }
+    if (core_config->pypackages_path) {
+        bufsz += wcslen(core_config->pypackages_path) + 1;
+    }
     if (calculate->machine_path) {
         bufsz += wcslen(calculate->machine_path) + 1;
     }
@@ -833,6 +836,15 @@ calculate_module_search_path(const _PyCoreConfig *core_config,
         buf = wcschr(buf, L'\0');
         *buf++ = DELIM;
     }
+    /* Adds the __pypackages__ directory */
+    if (core_config->pypackages_path) {
+        if (wcscpy_s(buf, bufsz - (buf - start_buf),
+                core_config->pypackages_path)) {
+                    return INIT_ERR_BUFFER_OVERFLOW();
+        }
+        buf = wcschr(buf, L'\0');
+        *buf++ = DELIM;
+    }
     if (calculate->zip_path[0]) {
         if (wcscpy_s(buf, bufsz - (buf - start_buf), calculate->zip_path)) {
             return INIT_ERR_BUFFER_OVERFLOW();

Note to self: From pypackages branch, see PEP-582.