allowed iter(cache), renamed .xy -> .data, commented .latest

cacher.py

@@ -43,16 +43,19 @@ class Cache:
         self.times.append(time())
         self.values.append(value)
 
-    @property
-    def xy(self):
-        return self.times, self.values
+    def __iter__(self):
+        return iter(self.data)
 
     @property
-    def latest(self):
-        try:
-            return self.values[-1]
-        except IndexError:
-            return None
+    def data(self):
+        return self.times, self.values
+
+#    @property
+#    def latest(self):
+#        try:
+#            return self.values[-1]
+#        except IndexError:
+#            return None
 
     def __repr__(self):
         n = len(self.times)