issue 9910

Add a Py_SetPath api to override magic path computations when starting up python.

Doc/c-api/init.rst

@@ -27,8 +27,9 @@ Initialization, Finalization, and Threads
 
    Initialize the Python interpreter.  In an application embedding  Python, this
    should be called before using any other Python/C API functions; with the
-   exception of :cfunc:`Py_SetProgramName`, :cfunc:`PyEval_InitThreads`,
-   :cfunc:`PyEval_ReleaseLock`, and :cfunc:`PyEval_AcquireLock`. This initializes
+   exception of :cfunc:`Py_SetProgramName`, :cfunc:`Py_SetPath`,
+   :cfunc:`PyEval_InitThreads`, :cfunc:`PyEval_ReleaseLock`, and
+   :cfunc:`PyEval_AcquireLock`. This initializes
    the table of loaded modules (``sys.modules``), and creates the fundamental
    modules :mod:`builtins`, :mod:`__main__` and :mod:`sys`.  It also initializes
    the module search path (``sys.path``). It does not set ``sys.argv``; use
@@ -256,6 +257,7 @@ Initialization, Finalization, and Threads
    .. index::
       triple: module; search; path
       single: path (in module sys)
+      single: Py_SetPath()
 
    Return the default module search path; this is computed from the program name
    (set by :cfunc:`Py_SetProgramName` above) and some environment variables.
@@ -270,6 +272,25 @@ Initialization, Finalization, and Threads
    .. XXX should give the exact rules
 
 
+.. cfunction::  void Py_SetPath(const wchar_t *)
+
+   .. index::
+      triple: module; search; path
+      single: path (in module sys)
+      single: Py_GetPath()
+
+   Set the default module search path.  If this function is called before
+   :cfunc: `Py_Initialize` then :cfunc: Py_GetPath won't attempt to compute
+   a default serarch path but uses the provided one in stead.  This is useful
+   if Python is being embedded by an application that has full knowledge
+   of the location of all modules.  The path components should be separated
+   by semicolons.
+
+   This also causes `sys.executable` to be set only to the raw program name
+   (see :cfunc:`Py_SetProgramName`) and `for sys.prefix` and
+   `sys.exec_prefix` to be empty.  It is up to the caller to modify these if
+   required after calling :cfunc: `Py_Initialize`.
+
 .. cfunction:: const char* Py_GetVersion()
 
    Return the version of this Python interpreter.  This is a string that looks

Include/pythonrun.h

@@ -113,6 +113,7 @@ PyAPI_FUNC(wchar_t *) Py_GetProgramFullPath(void);
 PyAPI_FUNC(wchar_t *) Py_GetPrefix(void);
 PyAPI_FUNC(wchar_t *) Py_GetExecPrefix(void);
 PyAPI_FUNC(wchar_t *) Py_GetPath(void);
+PyAPI_FUNC(void)      Py_SetPath(const wchar_t *);
 
 /* In their own files */
 PyAPI_FUNC(const char *) Py_GetVersion(void);

Modules/getpath.c

@@ -90,6 +90,9 @@
  * known use of sys.prefix and sys.exec_prefix is for the ILU installation
  * process to find the installed Python tree.
  *
+ * An embedding application can use Py_SetPath() to override all of
+ * these authomatic path computations.
+ *
  * NOTE: Windows MSVC builds use PC/getpathp.c instead!
  */
 
@@ -771,6 +774,23 @@ calculate_path(void)
 
 
 /* External interface */
+void
+Py_SetPath(const wchar_t *path)
+{
+    if (module_search_path != NULL) {
+        free(module_search_path);
+        module_search_path = NULL;
+    }
+    if (path != NULL) {
+        extern wchar_t *Py_GetProgramName(void);
+        wchar_t *prog = Py_GetProgramName();
+        wcsncpy(progpath, prog, MAXPATHLEN);
+        exec_prefix[0] = prefix[0] = L'\0';
+        module_search_path = malloc((wcslen(path) + 1) * sizeof(wchar_t));
+        if (module_search_path != NULL)
+            wcscpy(module_search_path, path);
+    }
+}
 
 wchar_t *
 Py_GetPath(void)

PC/getpathp.c

@@ -51,6 +51,9 @@
     exe, some very strange installation setup) you get a path with
     some default, but relative, paths.
 
+  * An embedding application can use Py_SetPath() to override all of
+    these authomatic path computations.
+
    ---------------------------------------------------------------- */
 
 
@@ -79,6 +82,9 @@
  * The approach is an adaptation for Windows of the strategy used in
  * ../Modules/getpath.c; it uses the Windows Registry as one of its
  * information sources.
+ *
+ * Py_SetPath() can be used to override this mechanism.  Call Py_SetPath
+ * with a semicolon separated path prior to calling Py_Initialize.
  */
 
 #ifndef LANDMARK
@@ -654,6 +660,24 @@ calculate_path(void)
 
 /* External interface */
 
+void
+Py_SetPath(const wchar_t *path)
+{
+    if (module_search_path != NULL) {
+        free(module_search_path);
+        module_search_path = NULL;
+    }
+    if (path != NULL) {
+        extern wchar_t *Py_GetProgramName(void);
+        wchar_t *prog = Py_GetProgramName();
+        wcsncpy(progpath, prog, MAXPATHLEN);
+        prefix[0] = L'\0';
+        module_search_path = malloc((wcslen(path) + 1) * sizeof(wchar_t));
+        if (module_search_path != NULL)
+            wcscpy(module_search_path, path);
+	}
+}
+
 wchar_t *
 Py_GetPath(void)
 {