# HG changeset patch
# Parent 69f58be4688a53338671c5ae6d93d49641719202
Issue #10433: Document unique behavior of 'os.getgroups' on Mac OS X.

diff --git a/Doc/library/os.rst b/Doc/library/os.rst
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -225,6 +225,20 @@
 
    Availability: Unix.
 
+   .. note:: On Mac OS X, getgroups() behavior differs somewhat from other Unix
+      platforms. If the Python interpreter was built with a deployment target
+      of 10.5 or earlier, getgroups() returns the list of effective group ids
+      associated with the current user process; this list is limited to a
+      system-defined number of entries, typically 16, and may be modified by
+      calls to :func:`setgroups` if suitably privileged. If built with a
+      deployment target greater than 10.5, getgroups() returns the
+      current group access list for the user associated with the effective
+      user id of the process; the group access list may change over the
+      lifetime of the process, it is not affected by calls to :func:`setgroups`,
+      and its length is not limited to 16.  The deployment target value,
+      :const:`MACOSX_DEPLOYMENT_TARGET`, can be obtained with
+      :func:`sysconf.get_config_var`.
+
 
 .. function:: initgroups(username, gid)
 
@@ -412,6 +426,10 @@
 
    Availability: Unix.
 
+   .. note:: On Mac OS X, the length of *groups* may not exceed the
+      system-defined maximum number of effective group ids, typically 16.
+      See the documentation for :func:`getgroups` for cases where it may not
+      return the same group list set by calling setgroups().
 
 .. function:: setpgrp()