[Python-checkins] bpo-42567: [Enum] call __init_subclass__ after members are added (GH-23714)
ethanfurman
webhook-mailer at python.org
Wed Dec 9 19:41:31 EST 2020
https://github.com/python/cpython/commit/6bd94de168b58ac9358277ed6f200490ab26c174
commit: 6bd94de168b58ac9358277ed6f200490ab26c174
branch: master
author: Ethan Furman <ethan at stoneleaf.us>
committer: ethanfurman <ethan at stoneleaf.us>
date: 2020-12-09T16:41:22-08:00
summary:
bpo-42567: [Enum] call __init_subclass__ after members are added (GH-23714)
When creating an Enum, type.__new__ calls __init_subclass__, but at that point the members have not been added.
This patch suppresses the initial call, then manually calls the ancestor __init_subclass__ before returning the new Enum class.
files:
A Misc/NEWS.d/next/Library/2020-12-08-22-43-35.bpo-42678.ba9ktU.rst
M Lib/enum.py
M Lib/test/test_enum.py
diff --git a/Lib/enum.py b/Lib/enum.py
index f6c7e8b233413..83e050e1e41cd 100644
--- a/Lib/enum.py
+++ b/Lib/enum.py
@@ -9,6 +9,14 @@
]
+class _NoInitSubclass:
+ """
+ temporary base class to suppress calling __init_subclass__
+ """
+ @classmethod
+ def __init_subclass__(cls, **kwds):
+ pass
+
def _is_descriptor(obj):
"""
Returns True if obj is a descriptor, False otherwise.
@@ -157,7 +165,7 @@ def __prepare__(metacls, cls, bases):
)
return enum_dict
- def __new__(metacls, cls, bases, classdict):
+ def __new__(metacls, cls, bases, classdict, **kwds):
# an Enum class is final once enumeration items have been defined; it
# cannot be mixed with other types (int, float, etc.) if it has an
# inherited __new__ unless a new __new__ is defined (or the resulting
@@ -192,8 +200,22 @@ def __new__(metacls, cls, bases, classdict):
if '__doc__' not in classdict:
classdict['__doc__'] = 'An enumeration.'
+ # postpone calling __init_subclass__
+ if '__init_subclass__' in classdict and classdict['__init_subclass__'] is None:
+ raise TypeError('%s.__init_subclass__ cannot be None')
+ # remove current __init_subclass__ so previous one can be found with getattr
+ new_init_subclass = classdict.pop('__init_subclass__', None)
# create our new Enum type
- enum_class = super().__new__(metacls, cls, bases, classdict)
+ if bases:
+ bases = (_NoInitSubclass, ) + bases
+ enum_class = type.__new__(metacls, cls, bases, classdict)
+ enum_class.__bases__ = enum_class.__bases__[1:] #or (object, )
+ else:
+ enum_class = type.__new__(metacls, cls, bases, classdict)
+ old_init_subclass = getattr(enum_class, '__init_subclass__', None)
+ # and restore the new one (if there was one)
+ if new_init_subclass is not None:
+ enum_class.__init_subclass__ = classmethod(new_init_subclass)
enum_class._member_names_ = [] # names in definition order
enum_class._member_map_ = {} # name->value map
enum_class._member_type_ = member_type
@@ -305,6 +327,9 @@ def __new__(metacls, cls, bases, classdict):
if _order_ != enum_class._member_names_:
raise TypeError('member order does not match _order_')
+ # finally, call parents' __init_subclass__
+ if Enum is not None and old_init_subclass is not None:
+ old_init_subclass(**kwds)
return enum_class
def __bool__(self):
@@ -682,6 +707,9 @@ def _generate_next_value_(name, start, count, last_values):
else:
return start
+ def __init_subclass__(cls, **kwds):
+ super().__init_subclass__(**kwds)
+
@classmethod
def _missing_(cls, value):
return None
diff --git a/Lib/test/test_enum.py b/Lib/test/test_enum.py
index ab4b52f785273..20bc5b3c750d6 100644
--- a/Lib/test/test_enum.py
+++ b/Lib/test/test_enum.py
@@ -2117,6 +2117,43 @@ class ThirdFailedStrEnum(StrEnum):
class ThirdFailedStrEnum(StrEnum):
one = '1'
two = b'2', 'ascii', 9
+
+ def test_init_subclass(self):
+ class MyEnum(Enum):
+ def __init_subclass__(cls, **kwds):
+ super(MyEnum, cls).__init_subclass__(**kwds)
+ self.assertFalse(cls.__dict__.get('_test', False))
+ cls._test1 = 'MyEnum'
+ #
+ class TheirEnum(MyEnum):
+ def __init_subclass__(cls, **kwds):
+ super().__init_subclass__(**kwds)
+ cls._test2 = 'TheirEnum'
+ class WhoseEnum(TheirEnum):
+ def __init_subclass__(cls, **kwds):
+ pass
+ class NoEnum(WhoseEnum):
+ ONE = 1
+ self.assertEqual(TheirEnum.__dict__['_test1'], 'MyEnum')
+ self.assertEqual(WhoseEnum.__dict__['_test1'], 'MyEnum')
+ self.assertEqual(WhoseEnum.__dict__['_test2'], 'TheirEnum')
+ self.assertFalse(NoEnum.__dict__.get('_test1', False))
+ self.assertFalse(NoEnum.__dict__.get('_test2', False))
+ #
+ class OurEnum(MyEnum):
+ def __init_subclass__(cls, **kwds):
+ cls._test2 = 'OurEnum'
+ class WhereEnum(OurEnum):
+ def __init_subclass__(cls, **kwds):
+ pass
+ class NeverEnum(WhereEnum):
+ ONE = 'one'
+ self.assertEqual(OurEnum.__dict__['_test1'], 'MyEnum')
+ self.assertFalse(WhereEnum.__dict__.get('_test1', False))
+ self.assertEqual(WhereEnum.__dict__['_test2'], 'OurEnum')
+ self.assertFalse(NeverEnum.__dict__.get('_test1', False))
+ self.assertFalse(NeverEnum.__dict__.get('_test2', False))
+
class TestOrder(unittest.TestCase):
@@ -2573,6 +2610,42 @@ def cycle_enum():
'at least one thread failed while creating composite members')
self.assertEqual(256, len(seen), 'too many composite members created')
+ def test_init_subclass(self):
+ class MyEnum(Flag):
+ def __init_subclass__(cls, **kwds):
+ super().__init_subclass__(**kwds)
+ self.assertFalse(cls.__dict__.get('_test', False))
+ cls._test1 = 'MyEnum'
+ #
+ class TheirEnum(MyEnum):
+ def __init_subclass__(cls, **kwds):
+ super(TheirEnum, cls).__init_subclass__(**kwds)
+ cls._test2 = 'TheirEnum'
+ class WhoseEnum(TheirEnum):
+ def __init_subclass__(cls, **kwds):
+ pass
+ class NoEnum(WhoseEnum):
+ ONE = 1
+ self.assertEqual(TheirEnum.__dict__['_test1'], 'MyEnum')
+ self.assertEqual(WhoseEnum.__dict__['_test1'], 'MyEnum')
+ self.assertEqual(WhoseEnum.__dict__['_test2'], 'TheirEnum')
+ self.assertFalse(NoEnum.__dict__.get('_test1', False))
+ self.assertFalse(NoEnum.__dict__.get('_test2', False))
+ #
+ class OurEnum(MyEnum):
+ def __init_subclass__(cls, **kwds):
+ cls._test2 = 'OurEnum'
+ class WhereEnum(OurEnum):
+ def __init_subclass__(cls, **kwds):
+ pass
+ class NeverEnum(WhereEnum):
+ ONE = 1
+ self.assertEqual(OurEnum.__dict__['_test1'], 'MyEnum')
+ self.assertFalse(WhereEnum.__dict__.get('_test1', False))
+ self.assertEqual(WhereEnum.__dict__['_test2'], 'OurEnum')
+ self.assertFalse(NeverEnum.__dict__.get('_test1', False))
+ self.assertFalse(NeverEnum.__dict__.get('_test2', False))
+
class TestIntFlag(unittest.TestCase):
"""Tests of the IntFlags."""
diff --git a/Misc/NEWS.d/next/Library/2020-12-08-22-43-35.bpo-42678.ba9ktU.rst b/Misc/NEWS.d/next/Library/2020-12-08-22-43-35.bpo-42678.ba9ktU.rst
new file mode 100644
index 0000000000000..7c94cdf40dd4c
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-12-08-22-43-35.bpo-42678.ba9ktU.rst
@@ -0,0 +1 @@
+`Enum`: call `__init_subclass__` after members have been added
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