Expose Py_Py3kWarningFlag as sys.py3kwarning as discussed in #1504
Also added a warning.warnpy3k() as convenient method for Python 3.x related deprecation warnings.
diff --git a/Doc/library/warnings.rst b/Doc/library/warnings.rst
index 6049f5d..6188195 100644
--- a/Doc/library/warnings.rst
+++ b/Doc/library/warnings.rst
@@ -200,6 +200,14 @@
was added in Python 2.5.)
+.. function:: warnpy3k(message[, category[, stacklevel]])
+
+ Issue a warning related to Python 3.x deprecation. Warnings are only shown
+ when Python is started with the -3 option. Like func:`warn` *message* must
+ be a string and *category* a subclass of :exc:`Warning`. :func:`warnpy3k`
+ is using :exc:`DeprecationWarning` as default warning class.
+
+
.. function:: showwarning(message, category, filename, lineno[, file])
Write a warning to a file. The default implementation calls