deprecate current behavior

Doc/library/enum.rst

@@ -761,6 +761,10 @@ Utilities and Decorators
  ``_generate_next_value_`` can be overridden to customize the values used by
  *auto*.
 
+ .. note:: in 3.13 the default ``"generate_next_value_`` will always return
+ the highest member value incremented by 1, and will fail if any
+ member is an incompatible type.
+
 .. decorator:: property
 
  A decorator similar to the built-in *property*, but specifically for

Lib/enum.py

@@ -1205,28 +1205,39 @@ def __new__(cls, value):
  def __init__(self, *args, **kwds):
  pass
 
- def _generate_next_value_(name, start, count, last_values):
+ def _generate_next_value_(name, start, count, last_value):
  """
  Generate the next value when not given.
 
  name: the name of the member
  start: the initial start value or None
  count: the number of existing members
- last_values: the list of values assigned
+ last_value: the list of values assigned
  """
-
- # Filter funciton to deal with last_values lists of mixed types
- def test_incrementable(n):
- try:
- n + 1
- return True
- except TypeError:
- return False
-
- checked_last_values = sorted(filter(test_incrementable, last_values))
- if checked_last_values:
- return checked_last_values[-1] + 1
- else:
+ if not last_value:
+ return start
+ try:
+ last = last_value[-1]
+ last_value.sort()
+ if last == last_value[-1]:
+ # no difference between old and new methods
+ return last + 1
+ else:
+ # trigger old method (with warning)
+ raise TypeError
+ except TypeError:
+ import warnings
+ warnings.warn(
+ "In 3.13 the default `auto()`/`_generate_next_value_` will require all values to be sortable and support adding +1\n"
+ "and the value returned will be the largest value in the enum incremented by 1",
+ DeprecationWarning,
+ stacklevel=3,
+ )
+ for v in last_value:
+ try:
+ return v + 1
+ except TypeError:
+ pass
  return start
 
  @classmethod

Lib/test/test_enum.py

@@ -3953,23 +3953,54 @@ class Color(AutoNameEnum):
  self.assertEqual(Color.blue.value, 'blue')
  self.assertEqual(Color.green.value, 'green')
 
- def test_auto_garbage(self):
- class Color(Enum):
- red = 'red'
- blue = auto()
+ @unittest.skipIf(
+ python_version >= (3, 13),
+ 'mixed types with auto() no longer supported',
+ )
+ def test_auto_garbage_ok(self):
+ with self.assertWarnsRegex(DeprecationWarning, 'will require all values to be sortable'):
+ class Color(Enum):
+ red = 'red'
+ blue = auto()
  self.assertEqual(Color.blue.value, 1)
 
- def test_auto_garbage_corrected(self):
- class Color(Enum):
- red = 'red'
- blue = 2
- green = auto()
+ @unittest.skipIf(
+ python_version >= (3, 13),
+ 'mixed types with auto() no longer supported',
+ )
+ def test_auto_garbage_corrected_ok(self):
+ with self.assertWarnsRegex(DeprecationWarning, 'will require all values to be sortable'):
+ class Color(Enum):
+ red = 'red'
+ blue = 2
+ green = auto()
 
  self.assertEqual(list(Color), [Color.red, Color.blue, Color.green])
  self.assertEqual(Color.red.value, 'red')
  self.assertEqual(Color.blue.value, 2)
  self.assertEqual(Color.green.value, 3)
 
+ @unittest.skipIf(
+ python_version < (3, 13),
+ 'mixed types with auto() will raise in 3.13',
+ )
+ def test_auto_garbage_fail(self):
+ with self.assertRaisesRegex(TypeError, 'will require all values to be sortable'):
+ class Color(Enum):
+ red = 'red'
+ blue = auto()
+
+ @unittest.skipIf(
+ python_version < (3, 13),
+ 'mixed types with auto() will raise in 3.13',
+ )
+ def test_auto_garbage_corrected_fail(self):
+ with self.assertRaisesRegex(TypeError, 'will require all values to be sortable'):
+ class Color(Enum):
+ red = 'red'
+ blue = 2
+ green = auto()
+
  def test_auto_order(self):
  with self.assertRaises(TypeError):
  class Color(Enum):
@@ -3991,6 +4022,10 @@ def _generate_next_value_(name, start, count, last):
  self.assertEqual(Color.red.value, 'pathological case')
  self.assertEqual(Color.blue.value, 'blue')
 
+ @unittest.skipIf(
+ python_version < (3, 13),
+ 'auto() will return highest value + 1 in 3.13',
+ )
  def test_auto_with_aliases(self):
  class Color(Enum):
  red = auto()

Misc/NEWS.d/next/Library/2022-04-11-16-55-41.gh-issue-91456.DK3KKl.rst

@@ -1,2 +1,3 @@
-Fixed an issue with Enums where the default behavior of auto() was
-generating incorrect values following alias assignment
+Deprecate current default auto() behavior: In 3.13 the default will be for
+for auto() to always return the largest member value incremented by
+1, and to raise if incompatible value types are used.