bpo-36085: Enable better DLL resolution on Windows (GH-12302)

Doc/library/os.rst

@@ -3079,6 +3079,36 @@ to be ignored.
    :func:`signal.signal`.
 
 
+.. function:: add_dll_directory(path)
+
+   Add a path to the DLL search path.
+
+   This search path is used when resolving dependencies for imported
+   extension modules (the module itself is resolved through sys.path),
+   and also by :mod:`ctypes`.
+
+   Remove the directory by calling **close()** on the returned object
+   or using it in a :keyword:`with` statement.
+
+   See the `Microsoft documentation
+   <https://msdn.microsoft.com/44228cf2-6306-466c-8f16-f513cd3ba8b5>`_
+   for more information about how DLLs are loaded.
+
+   .. availability:: Windows.
+
+   .. versionadded:: 3.8
+      Previous versions of CPython would resolve DLLs using the default
+      behavior for the current process. This led to inconsistencies,
+      such as only sometimes searching :envvar:`PATH` or the current
+      working directory, and OS functions such as ``AddDllDirectory``
+      having no effect.
+
+      In 3.8, the two primary ways DLLs are loaded now explicitly
+      override the process-wide behavior to ensure consistency. See the
+      :ref:`porting notes <bpo-36085-whatsnew>` for information on
+      updating libraries.
+
+
 .. function:: execl(path, arg0, arg1, ...)
               execle(path, arg0, arg1, ..., env)
               execlp(file, arg0, arg1, ...)