Change PriorityQueue expansion (#962)

D-K-E · norvig · commit eee83f6489c5 · 2018-09-27T22:32:51.000-07:00
`self.heap.append` simply appends to the end of the `self.heap` 
Since `self.heap` is just a python list. 
`self.append` calls the append method of the class instance, effectively putting the item in its proper place.
diff --git a/utils.py b/utils.py
@@ -717,7 +717,7 @@ def append(self, item):
     def extend(self, items):
         """Insert each item in items at its correct position."""
         for item in items:
-            self.heap.append(item)
+            self.append(item)
 
     def pop(self):
         """Pop and return the item (with min or max f(x) value
