Replace mentions of IOError
diff --git a/Doc/library/urllib.error.rst b/Doc/library/urllib.error.rst
index 793d3e2..e20db27 100644
--- a/Doc/library/urllib.error.rst
+++ b/Doc/library/urllib.error.rst
@@ -8,20 +8,23 @@
The :mod:`urllib.error` module defines the exception classes for exceptions
-raised by :mod:`urllib.request`. The base exception class is :exc:`URLError`,
-which inherits from :exc:`IOError`.
+raised by :mod:`urllib.request`. The base exception class is :exc:`URLError`.
The following exceptions are raised by :mod:`urllib.error` as appropriate:
.. exception:: URLError
The handlers raise this exception (or derived exceptions) when they run into
- a problem. It is a subclass of :exc:`IOError`.
+ a problem. It is a subclass of :exc:`OSError`.
.. attribute:: reason
The reason for this error. It can be a message string or another
- exception instance such as :exc:`OSError`.
+ exception instance.
+
+ .. versionchanged:: 3.3
+ :exc:`URLError` has been made a subclass of :exc:`OSError` instead
+ of :exc:`IOError`.
.. exception:: HTTPError