Add UserList.discard() to match list

Author: StanFromIreland

Lib/collections/__init__.py

@@ -1386,6 +1386,9 @@ def pop(self, i=-1):
     def remove(self, item):
         self.data.remove(item)
 
+    def discard(self, item):
+        self.data.discard(item)
+
     def clear(self):
         self.data.clear()
 

Lib/test/list_tests.py

@@ -373,6 +373,66 @@ def __eq__(self, other):
             # verify that original order and values are retained.
             self.assertIs(x, y)
 
+    def test_discard(self):
+        a = self.type2test([0, 0, 1])
+        a.discard(1)
+        self.assertEqual(a, self.type2test([0, 0]))
+        a.discard(0)
+        self.assertEqual(a, self.type2test([0]))
+        a.discard(0)
+        self.assertEqual(a, self.type2test([]))
+        a.discard(0)
+        self.assertEqual(a, self.type2test([]))
+
+        self.assertRaises(TypeError, a.discard)
+
+        a = self.type2test([1, 2])
+        a.discard(NEVER_EQ)
+        self.assertEqual(a, self.type2test([1, 2]))
+        a.discard(ALWAYS_EQ)
+        self.assertEqual(a, self.type2test([2]))
+        a = self.type2test([ALWAYS_EQ])
+        a.discard(1)
+        self.assertEqual(a, self.type2test([]))
+        a = self.type2test([ALWAYS_EQ])
+        a.discard(NEVER_EQ)
+        self.assertEqual(a, self.type2test([]))
+        a = self.type2test([NEVER_EQ])
+        a.discard(ALWAYS_EQ)
+        self.assertEqual(a, self.type2test([NEVER_EQ]))
+
+        class BadExc(Exception):
+            pass
+
+        class BadCmp:
+            def __eq__(self, other):
+                if other == 2:
+                    raise BadExc()
+                return False
+
+        a = self.type2test([0, 1, 2, 3])
+        self.assertRaises(BadExc, a.discard, BadCmp())
+
+        class BadCmp2:
+            def __eq__(self, other):
+                raise BadExc()
+
+        d = self.type2test('abcdefghcij')
+        d.discard('c')
+        self.assertEqual(d, self.type2test('abdefghcij'))
+        d.discard('c')
+        self.assertEqual(d, self.type2test('abdefghij'))
+        d.discard('c')
+        self.assertEqual(d, self.type2test('abdefghij'))
+
+        # Handle comparison errors
+        d = self.type2test(['a', 'b', BadCmp2(), 'c'])
+        e = self.type2test(d)
+        self.assertRaises(BadExc, d.discard, 'c')
+        for x, y in zip(d, e):
+            # verify that original order and values are retained.
+            self.assertIs(x, y)
+
     def test_index(self):
         super().test_index()
         a = self.type2test([-2, -1, 0, 0, 1, 2])

Lib/test/test_descrtut.py

@@ -209,6 +209,7 @@ def merge(self, other):
      'clear',
      'copy',
      'count',
+     'discard',
      'extend',
      'index',
      'insert',

Lib/test/test_list.py

@@ -2,7 +2,7 @@
 import sys
 import textwrap
 from test import list_tests, support
-from test.support import ALWAYS_EQ, NEVER_EQ, cpython_only
+from test.support import cpython_only
 from test.support.script_helper import assert_python_failure, assert_python_ok
 import pickle
 import unittest
@@ -331,66 +331,6 @@ def test_preallocation(self):
         self.assertEqual(iter_size, sys.getsizeof(list([0] * 10)))
         self.assertEqual(iter_size, sys.getsizeof(list(range(10))))
 
-    def test_discard(self):
-        a = [0, 0, 1]
-        a.discard(1)
-        self.assertEqual(a, [0, 0])
-        a.discard(0)
-        self.assertEqual(a, [0])
-        a.discard(0)
-        self.assertEqual(a, [])
-        a.discard(0)
-        self.assertEqual(a, [])
-
-        self.assertRaises(TypeError, a.discard)
-
-        a = [1, 2]
-        a.discard(NEVER_EQ)
-        self.assertEqual(a, [1, 2])
-        a.discard(ALWAYS_EQ)
-        self.assertEqual(a, [2])
-        a = [ALWAYS_EQ]
-        a.discard(1)
-        self.assertEqual(a, [])
-        a = [ALWAYS_EQ]
-        a.discard(NEVER_EQ)
-        self.assertEqual(a, [])
-        a = [NEVER_EQ]
-        a.discard(ALWAYS_EQ)
-        self.assertEqual(a, [NEVER_EQ])
-
-        class BadExc(Exception):
-            pass
-
-        class BadCmp:
-            def __eq__(self, other):
-                if other == 2:
-                    raise BadExc()
-                return False
-
-        a = [0, 1, 2, 3]
-        self.assertRaises(BadExc, a.discard, BadCmp())
-
-        class BadCmp2:
-            def __eq__(self, other):
-                raise BadExc()
-
-        d = list('abcdefghcij')
-        d.discard('c')
-        self.assertEqual(d, list('abdefghcij'))
-        d.discard('c')
-        self.assertEqual(d, list('abdefghij'))
-        d.discard('c')
-        self.assertEqual(d, list('abdefghij'))
-
-        # Handle comparison errors
-        d = ['a', 'b', BadCmp2(), 'c']
-        e = list(d)
-        self.assertRaises(BadExc, d.discard, 'c')
-        for x, y in zip(d, e):
-            # verify that original order and values are retained.
-            self.assertIs(x, y)
-
     def test_count_index_remove_crashes(self):
         # bpo-38610: The count(), index(), and remove() methods were not
         # holding strong references to list elements while calling