Handle the update of an element that had collided with a deleted item

Author: bzaczynski

hashtable/02_linear_probing/hashtable.py

@@ -43,7 +43,8 @@ def __delitem__(self, key):
 
     def __setitem__(self, key, value):
         for index, pair in self._probe(key):
-            if pair in (None, DELETED) or pair.key == key:
+            if pair is DELETED: continue
+            if pair is None or pair.key == key:
                 self._slots[index] = Pair(key, value)
                 break
         else:

hashtable/02_linear_probing/test_hashtable.py

@@ -333,7 +333,7 @@ def test_should_wrap_index_around_when_collides(mock_hash):
     assert hash_table._slots[0] == (False, True)
 
 
-def test_should_overwrite_deleted(hash_table):
+def test_should_not_overwrite_deleted(hash_table):
     del hash_table["hola"]
     deleted_slot = hash_table._slots.index(DELETED)
 
@@ -344,7 +344,7 @@ def test_should_overwrite_deleted(hash_table):
         hash_table["gracias"] = "thank you"
 
     assert len(hash_table) == 3
-    assert DELETED not in hash_table._slots
+    assert DELETED in hash_table._slots
 
 
 def test_should_raise_memory_error_when_not_enough_capacity():

hashtable/03_autoresize/hashtable.py

@@ -43,7 +43,8 @@ def __delitem__(self, key):
 
     def __setitem__(self, key, value):
         for index, pair in self._probe(key):
-            if pair in (None, DELETED) or pair.key == key:
+            if pair is DELETED: continue
+            if pair is None or pair.key == key:
                 self._slots[index] = Pair(key, value)
                 break
         else:

hashtable/03_autoresize/test_hashtable.py

@@ -337,7 +337,7 @@ def test_should_wrap_index_around_when_collides(mock_hash):
     assert hash_table._slots[0] == (False, True)
 
 
-def test_should_overwrite_deleted(hash_table):
+def test_should_not_overwrite_deleted(hash_table):
     del hash_table["hola"]
     deleted_slot = hash_table._slots.index(DELETED)
 
@@ -348,7 +348,7 @@ def test_should_overwrite_deleted(hash_table):
         hash_table["gracias"] = "thank you"
 
     assert len(hash_table) == 3
-    assert DELETED not in hash_table._slots
+    assert DELETED in hash_table._slots
 
 
 def test_should_double_capacity():

hashtable/04_load_factor/hashtable.py

@@ -49,7 +49,8 @@ def __setitem__(self, key, value):
             self._resize_and_rehash()
 
         for index, pair in self._probe(key):
-            if pair in (None, DELETED) or pair.key == key:
+            if pair is DELETED: continue
+            if pair is None or pair.key == key:
                 self._slots[index] = Pair(key, value)
                 break
 

hashtable/04_load_factor/test_hashtable.py

@@ -360,7 +360,7 @@ def test_should_wrap_index_around_when_collides(mock_hash):
     assert hash_table._slots[0] == (False, True)
 
 
-def test_should_overwrite_deleted(hash_table):
+def test_should_not_overwrite_deleted(hash_table):
     del hash_table["hola"]
     deleted_slot = hash_table._slots.index(DELETED)
 
@@ -371,7 +371,7 @@ def test_should_overwrite_deleted(hash_table):
         hash_table["gracias"] = "thank you"
 
     assert len(hash_table) == 3
-    assert DELETED not in hash_table._slots
+    assert DELETED in hash_table._slots
 
 
 def test_should_double_capacity():