deal with sentinel point

Author: miachang

pygtrie.py

@@ -1372,6 +1372,10 @@ def discard(self, key):
         if node and node.children:
             for child in node.children:
                 self.discard(child)
+        else:
+            node.children = {}
+            node.value = _SENTINEL
+        
 
 
     # Raises KeyError if elem is not contained in the set.
@@ -1384,6 +1388,9 @@ def remove(self, key):
         if node and node.children:
             for child in node.children:
                 self.discard(child)
+        else:
+            node.children = {}
+            node.value = _SENTINEL
 
     def pop(self):