bpo-39728: enum with invalid value results in ValueError twice

Andrey Darascheka · Andrey Darascheka · commit ca86aff48d3d · 2020-02-24T10:59:02.000+03:00
diff --git a/Lib/enum.py b/Lib/enum.py
@@ -585,7 +585,6 @@ def __new__(cls, value):
                         'error in %s._missing_: returned %r instead of None or a valid member'
                         % (cls.__name__, result)
                         )
-            exc.__context__ = ve_exc
             raise exc
 
     def _generate_next_value_(name, start, count, last_values):
diff --git a/Lib/test/test_enum.py b/Lib/test/test_enum.py
@@ -1776,19 +1776,12 @@ def _missing_(cls, item):
                     # trigger not found
                     return None
         self.assertIs(Color('three'), Color.blue)
-        self.assertRaises(ValueError, Color, 7)
-        try:
+        with self.assertRaises(ValueError):
+            Color(7)
+        with self.assertRaises(TypeError):
             Color('bad return')
-        except TypeError as exc:
-            self.assertTrue(isinstance(exc.__context__, ValueError))
-        else:
-            raise Exception('Exception not raised.')
-        try:
+        with self.assertRaises(ZeroDivisionError):
             Color('error out')
-        except ZeroDivisionError as exc:
-            self.assertTrue(isinstance(exc.__context__, ValueError))
-        else:
-            raise Exception('Exception not raised.')
 
     def test_multiple_mixin(self):
         class MaxMixin:
diff --git a/Misc/NEWS.d/next/Library/2020-02-24-10-58-34.bpo-39728.kOOaHn.rst b/Misc/NEWS.d/next/Library/2020-02-24-10-58-34.bpo-39728.kOOaHn.rst
@@ -0,0 +1 @@
+Instantiating enum with invalid value results in ValueError twice

Original file line number	Diff line number	Diff line change
`@@ -585,7 +585,6 @@ def __new__(cls, value):`
`585`	`585`	`'error in %s._missing_: returned %r instead of None or a valid member'`
`586`	`586`	`% (cls.__name__, result)`
`587`	`587`	`)`
`588`		`- exc.__context__ = ve_exc`
`589`	`588`	`raise exc`
`590`	`589`
`591`	`590`	`def _generate_next_value_(name, start, count, last_values):`
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1 @@`
	`1`	`+Instantiating enum with invalid value results in ValueError twice`