Issue #23955: Add pyvenv.cfg option to suppress registry/environment lookup for…

Issue #23955: Add pyvenv.cfg option to suppress registry/environment lookup for generating sys.path.
Also cleans up and secures getpathp.c

Doc/using/windows.rst

@@ -661,6 +661,17 @@ This is how :data:`sys.path` is populated on Windows:
   the environment, and no registry entries can be found, a default path with
   relative entries is used (e.g. ``.\Lib;.\plat-win``, etc).
 
+If a ``pyvenv.cfg`` file is found alongside the main executable or in the
+directory one level above the executable, the following variations apply:
+
+* If ``home`` is an absolute path and :envvar:`PYTHONHOME` is not set, this
+  path is used instead of the path to the main executable when deducing the
+  home location.
+
+* If ``applocal`` is set to true, the ``home`` property or the main executable
+  is always used as the home path, and all environment variables or registry
+  values affecting the path are ignored. The landmark file is not checked.
+
 The end result of all this is:
 
 * When running :file:`python.exe`, or any other .exe in the main Python
@@ -672,13 +683,17 @@ The end result of all this is:
   etc), the "Python Home" will not be deduced, so the core path from the
   registry is used.  Other "application paths" in the registry are always read.
 
-* If Python can't find its home and there is no registry (eg, frozen .exe, some
-  very strange installation setup) you get a path with some default, but
+* If Python can't find its home and there are no registry value (frozen .exe,
+  some very strange installation setup) you get a path with some default, but
   relative, paths.
 
 For those who want to bundle Python into their application or distribution, the
 following advice will prevent conflicts with other installations:
 
+* Include a ``pyvenv.cfg`` file alongside your executable containing
+  ``applocal = true``. This will ensure that your own directory will be used to
+  resolve paths even if you have included the standard library in a ZIP file.
+
 * If you are loading :file:`python3.dll` or :file:`python35.dll` in your own
   executable, explicitly call :c:func:`Py_SetPath` or (at least)
   :c:func:`Py_SetProgramName` before :c:func:`Py_Initialize`.
@@ -688,7 +703,7 @@ following advice will prevent conflicts with other installations:
 
 * If you cannot use the previous suggestions (for example, you are a
   distribution that allows people to run :file:`python.exe` directly), ensure
-  that the landmark file (:file:`Lib\\os.py`) exists in your bundled library.
+  that the landmark file (:file:`Lib\\os.py`) exists in your install directory.
   (Note that it will not be detected inside a ZIP file.)
 
 These will ensure that the files in a system-wide installation will not take

Misc/NEWS

@@ -10,6 +10,9 @@ Release date: 2015-05-24
 Core and Builtins
 -----------------
 
+- Issue #23955: Add pyvenv.cfg option to suppress registry/environment
+  lookup for generating sys.path on Windows.
+
 - Issue #24257: Fixed system error in the comparison of faked
   types.SimpleNamespace.
 

Tools/msi/make_zip.py

@@ -149,6 +149,9 @@ def main():
             copied = copy_to_layout(temp / t.rstrip('/'), rglob(s, p, c))
             print('Copied {} files'.format(copied))
 
+        with open(str(temp / 'pyvenv.cfg'), 'w') as f:
+            print('applocal = true', file=f)
+
         total = copy_to_layout(out, rglob(temp, '*', None))
         print('Wrote {} files to {}'.format(total, out))
     finally: