py: Fix delete operation on map/dict and set objects.

Hash table can now be completely full (ie now NULL entry) before a
resize is triggered.  Use sentinel value to indicate delete entry in the
table.

tests/basics/dict-del.py

@@ -1,8 +1,21 @@
-for i in range(100):
-    d = dict()
-    for j in range(100):
-        d[j] = j
-    del d[i]
-    for j in range(100):
-        if j not in d:
-            print(j, 'not in d')
+for n in range(20):
+    print('testing dict with {} items'.format(n))
+    for i in range(n):
+        # create dict
+        d = dict()
+        for j in range(n):
+            d[str(j)] = j
+        print(len(d))
+
+        # delete an item
+        del d[str(i)]
+        print(len(d))
+
+        # check items
+        for j in range(n):
+            if str(j) in d:
+                if j == i:
+                    print(j, 'in d, but it should not be')
+            else:
+                if j != i:
+                    print(j, 'not in d, but it should be')

tests/basics/set_remove.py

@@ -1,3 +1,4 @@
+# basic test
 s = {1}
 print(s.remove(1))
 print(list(s))
@@ -7,3 +8,26 @@ except KeyError:
     pass
 else:
     print("failed to raise KeyError")
+
+# test sets of varying size
+for n in range(20):
+    print('testing set with {} items'.format(n))
+    for i in range(n):
+        # create set
+        s = set()
+        for j in range(n):
+            s.add(str(j))
+        print(len(s))
+
+        # delete an item
+        s.remove(str(i))
+        print(len(s))
+
+        # check items
+        for j in range(n):
+            if str(j) in s:
+                if j == i:
+                    print(j, 'in s, but it should not be')
+            else:
+                if j != i:
+                    print(j, 'not in s, but it should be')