diff --git a/fields/computed.py b/fields/computed.py
index 37418e8..30fc6e9 100644
--- a/fields/computed.py
+++ b/fields/computed.py
@@ -49,7 +49,7 @@ class Computed(Field):
                  maxChars=None, colspan=1, method=None, plainText=False,
                  master=None, masterValue=None, focus=False, historized=False,
                  sync=True, mapping=None, label=None, sdefault='', scolspan=1,
-                 swidth=None, sheight=None, context={}):
+                 swidth=None, sheight=None, context=None):
         # The Python method used for computing the field value, or a PX.
         self.method = method
         # Does field computation produce plain text or XHTML?
@@ -74,7 +74,7 @@ class Computed(Field):
             obj = obj.appy()
             ctx = {'obj': obj, 'field': self,
                    '_': obj.translate, 'tool': obj.tool}
-            ctx.update(self.context)
+            if self.context: ctx.update(self.context)
             return self.method(ctx)
         else:
             # self.method is a method that will return the field value
diff --git a/gen/wrappers/__init__.py b/gen/wrappers/__init__.py
index dc75a03..f4a0bfb 100644
--- a/gen/wrappers/__init__.py
+++ b/gen/wrappers/__init__.py
@@ -1026,6 +1026,25 @@ class AbstractWrapper(object):
            whose values are the previous field values.'''
         self.o.addDataChange(data)
 
+    def getLastEvent(self, transition, notBefore=''):
+        '''Gets, from the object history, the last occurrence of transition
+           named p_transition. p_transition can be a list of names: in this
+           case, it returns the most recent occurrence of those transitions. If
+           p_notBefore is given, it corresponds to a kind of start transition
+           for the search: we will not search in the history preceding the last
+           occurrence of this transition.'''
+        history = self.history
+        i = len(history)-1
+        while i >= 0:
+            event = history[i]
+            if notBefore and (event['action'] == notBefore): return
+            if isinstance(transition, basestring):
+                condition = event['action'] == transition
+            else:
+                condition = event['action'] in transition
+            if condition: return event
+            i -= 1
+
     def formatText(self, text, format='html'):
         '''Produces a representation of p_text into the desired p_format, which
            is 'html' by default.'''