From a5828a6b6ddf8e73b59447753e79a6f62afef13d Mon Sep 17 00:00:00 2001
From: Ethan Furman <ethan@stoneleaf.us>
Date: Wed, 28 Feb 2024 13:10:22 -0800
Subject: [PATCH 1/2] fix by-value calls when second value is falsey; e.g.
 Cardinal(1, 0)

---
 Lib/enum.py                                       | 15 +++++++++++----
 Lib/test/test_enum.py                             |  9 +++++++++
 ...2024-02-28-13-10-17.gh-issue-116040.wDidHd.rst |  1 +
 3 files changed, 21 insertions(+), 4 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2024-02-28-13-10-17.gh-issue-116040.wDidHd.rst

diff --git a/Lib/enum.py b/Lib/enum.py
index d10b99615981ba..432f6c2701f4ba 100644
--- a/Lib/enum.py
+++ b/Lib/enum.py
@@ -162,6 +162,13 @@ def _dedent(text):
         lines[j] = l[i:]
     return '\n'.join(lines)
 
+class _not_given:
+    def __repr__(self):
+        return('<not given>')
+    def __bool__(self):
+        return False
+_not_given = _not_given()
+
 class _auto_null:
     def __repr__(self):
         return '_auto_null'
@@ -677,7 +684,7 @@ def __bool__(cls):
         """
         return True
 
-    def __call__(cls, value, names=None, *values, module=None, qualname=None, type=None, start=1, boundary=None):
+    def __call__(cls, value, names=_not_given, *values, module=None, qualname=None, type=None, start=1, boundary=None):
         """
         Either returns an existing member, or creates a new enum class.
 
@@ -706,18 +713,18 @@ def __call__(cls, value, names=None, *values, module=None, qualname=None, type=N
         """
         if cls._member_map_:
             # simple value lookup if members exist
-            if names:
+            if names is not _not_given:
                 value = (value, names) + values
             return cls.__new__(cls, value)
         # otherwise, functional API: we're creating a new Enum type
-        if names is None and type is None:
+        if names is _not_given and type is None:
             # no body? no data-type? possibly wrong usage
             raise TypeError(
                     f"{cls} has no members; specify `names=()` if you meant to create a new, empty, enum"
                     )
         return cls._create_(
                 class_name=value,
-                names=names,
+                names=names or None,
                 module=module,
                 qualname=qualname,
                 type=type,
diff --git a/Lib/test/test_enum.py b/Lib/test/test_enum.py
index cf3e042de1a4b4..3c8f9c6a97cbd9 100644
--- a/Lib/test/test_enum.py
+++ b/Lib/test/test_enum.py
@@ -3409,6 +3409,15 @@ def __new__(cls, int_value, *value_aliases):
         self.assertIs(Types(2), Types.NetList)
         self.assertIs(Types('nl'), Types.NetList)
 
+    def test_second_tuple_item_is_falsey(self):
+        class Cardinal(Enum):
+            RIGHT = (1, 0)
+            UP = (0, 1)
+            LEFT = (-1, 0)
+            DOWN = (0, -1)
+        Cardinal(1, 0)
+        Cardinal(-1, 0)
+
 
 class TestOrder(unittest.TestCase):
     "test usage of the `_order_` attribute"
diff --git a/Misc/NEWS.d/next/Library/2024-02-28-13-10-17.gh-issue-116040.wDidHd.rst b/Misc/NEWS.d/next/Library/2024-02-28-13-10-17.gh-issue-116040.wDidHd.rst
new file mode 100644
index 00000000000000..907b58b3a5c206
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2024-02-28-13-10-17.gh-issue-116040.wDidHd.rst
@@ -0,0 +1 @@
+[Enum] fix by-value calls when second value is falsey; e.g. Cardinal(1, 0)

From 248bd2c43298b6f39c0bcfe3bff572e3ed997fbe Mon Sep 17 00:00:00 2001
From: Ethan Furman <ethan@stoneleaf.us>
Date: Mon, 4 Mar 2024 12:40:29 -0800
Subject: [PATCH 2/2] address review comments

---
 Lib/test/test_enum.py | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/Lib/test/test_enum.py b/Lib/test/test_enum.py
index 68d1e2ec20fa01..0a44b61e9049ed 100644
--- a/Lib/test/test_enum.py
+++ b/Lib/test/test_enum.py
@@ -3415,8 +3415,8 @@ class Cardinal(Enum):
             UP = (0, 1)
             LEFT = (-1, 0)
             DOWN = (0, -1)
-        Cardinal(1, 0)
-        Cardinal(-1, 0)
+        self.assertIs(Cardinal(1, 0), Cardinal.RIGHT)
+        self.assertIs(Cardinal(-1, 0), Cardinal.LEFT)
 
     def test_no_members(self):
         with self.assertRaisesRegex(
@@ -3430,6 +3430,20 @@ def test_no_members(self):
             ):
             Flag(7)
 
+    def test_empty_names(self):
+        for nothing, e_type in (
+                ('', None),
+                ('', int),
+                ([], None),
+                ([], int),
+                ({}, None),
+                ({}, int),
+            ):
+            empty_enum = Enum('empty_enum', nothing, type=e_type)
+            self.assertEqual(len(empty_enum), 0)
+            self.assertRaises(TypeError, 'has no members', empty_enum, 0)
+
+
 class TestOrder(unittest.TestCase):
     "test usage of the `_order_` attribute"