[util] extend CustomNone with an __index__ method (#6009)

- Make it compatible with functions expecting integer arguments
- Simplify and reuse some method definitions

test/test_util.py

@@ -12,6 +12,7 @@ import sys
 import unittest
 
 import io
+import time
 import random
 import string
 import datetime
@@ -741,6 +742,9 @@ def hash(value):
 
         self.assertFalse(obj)
         self.assertEqual(len(obj), 0)
+        self.assertEqual(int(obj), 0)
+        self.assertEqual(hash(obj), 0)
+
         self.assertEqual(str(obj), str(None))
         self.assertEqual(repr(obj), repr(None))
         self.assertEqual(format(obj), str(None))
@@ -751,6 +755,7 @@ def hash(value):
         self.assertIs(obj(), obj)
         self.assertIs(obj(1, "a"), obj)
         self.assertIs(obj(foo="bar"), obj)
+        self.assertIs(iter(obj), obj)
         self.assertEqual(util.json_dumps(obj), "null")
 
         self.assertLess(obj, "foo")
@@ -797,6 +802,12 @@ def hash(value):
         mapping = {}
         mapping[obj] = 123
         self.assertIn(obj, mapping)
+        self.assertEqual(mapping[obj], 123)
+
+        array = [1, 2, 3]
+        self.assertEqual(array[obj], 1)
+
+        self.assertTrue(time.localtime(obj))
 
         i = 0
         for _ in obj: