diff -r 0238cc842805 Doc/library/sched.rst
--- a/Doc/library/sched.rst	Thu Dec 06 17:49:58 2012 -0500
+++ b/Doc/library/sched.rst	Sat Dec 08 12:16:53 2012 +0200
@@ -58,7 +58,7 @@
 :class:`scheduler` instances have the following methods and attributes:
 
 
-.. method:: scheduler.enterabs(time, priority, action, argument=[], kwargs={})
+.. method:: scheduler.enterabs(time, priority, action, argument=(), kwargs=None)
 
    Schedule a new event. The *time* argument should be a numeric type compatible
    with the return value of the *timefunc* function passed  to the constructor.
@@ -67,7 +67,8 @@
 
    Executing the event means executing ``action(*argument, **kwargs)``.
    *argument* must be a sequence holding the parameters for *action*.
-   *kwargs* must be a dictionary holding the keyword parameters for *action*.
+   *kwargs* must be a dictionary holding the keyword parameters for *action*
+   (an empty dictionary used if not specified).
 
    Return value is an event which may be used for later cancellation of the event
    (see :meth:`cancel`).
@@ -79,7 +80,7 @@
       *kwargs* parameter was added.
 
 
-.. method:: scheduler.enter(delay, priority, action, argument=[], kwargs={})
+.. method:: scheduler.enter(delay, priority, action, argument=(), kwargs=None)
 
    Schedule an event for *delay* more time units. Other than the relative time, the
    other arguments, the effect and the return value are the same as those for
diff -r 0238cc842805 Lib/sched.py
--- a/Lib/sched.py	Thu Dec 06 17:49:58 2012 -0500
+++ b/Lib/sched.py	Sat Dec 08 12:16:53 2012 +0200
@@ -60,24 +60,28 @@
         self.timefunc = timefunc
         self.delayfunc = delayfunc
 
-    def enterabs(self, time, priority, action, argument=[], kwargs={}):
+    def enterabs(self, time, priority, action, argument=(), kwargs=None):
         """Enter a new event in the queue at an absolute time.
 
         Returns an ID for the event which can be used to remove it,
         if necessary.
 
         """
+        if kwargs is None:
+            kwargs = {}
         with self._lock:
             event = Event(time, priority, action, argument, kwargs)
             heapq.heappush(self._queue, event)
             return event # The ID
 
-    def enter(self, delay, priority, action, argument=[], kwargs={}):
+    def enter(self, delay, priority, action, argument=(), kwargs=None):
         """A variant that specifies the time as a relative time.
 
         This is actually the more commonly used interface.
 
         """
+        if kwargs is None:
+            kwargs = {}
         with self._lock:
             time = self.timefunc() + delay
             return self.enterabs(time, priority, action, argument, kwargs)