isEmpty tested; extract fixed

Author: yyl

unit3/doublyLinkedList.py

@@ -59,12 +59,18 @@ def getLast(self):
       raise ContainerEmpty
     return self._tail
 
+  def getIsEmpty(self):
+    return not self._head
+
   first = property(
       fget = lambda self: self.getFirst())
 
   last = property(
       fget = lambda self: self.getLast())
 
+  isEmpty = property(
+      fget = lambda self: self.getIsEmpty())
+
   def append(self, obj):
     tmp = self.Element(self._tail, obj, None, self)
     if self._head == None or self._tail == None:
@@ -92,13 +98,15 @@ def extract(self, obj):
     prev = tmp
     while tmp != None:
       if tmp._value == obj:
-        if tmp == self._head:
-          tmp._next._prev = None
-          self._head = tmp._next
+        if tmp == self._head and tmp == self._tail:
+          self.purge()
         elif tmp == self._tail:
           tmp._prev = None
           prev._next = None
           self._tail = prev
+        elif tmp == self._head:
+          tmp._next._prev = None
+          self._head = tmp._next
         else:
           prev._next = tmp._next
           tmp._prev = None
@@ -116,3 +124,4 @@ def __copy__(self):
       tmp.append(current.value)
       current = current._next
     return tmp
+

unit3/test.py

@@ -62,6 +62,14 @@ def test_copy(self):
     self.assertEqual(a.head.value, 1)
     self.assertEqual(a.tail.value, 3)
 
+  def test_empty(self):
+    self.assertTrue(self.l.isEmpty)
+    self.l.append(1)
+    self.assertFalse(self.l.isEmpty)
+    self.l.extract(1)
+    self.assertTrue(self.l.isEmpty)
+
+
 
 if __name__ == "__main__":
   unittest.main()