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bpo-29577: Enum: mixin classes don't mix well with already mixed Enums (GH-9328) 

* bpo-29577: allow multiple mixin classes
This commit is contained in:
Ethan Furman 2018-09-21 19:03:09 -07:00 committed by GitHub
parent fd97d1f1af
commit 5bdab641da
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4 changed files with 228 additions and 33 deletions
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13
Doc/library/enum.rst
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@ -387,10 +387,17 @@ whatever value(s) were given to the enum member will be passed into those
methods. See `Planet`_ for an example.
Restricted subclassing of enumerations
--------------------------------------
Restricted Enum subclassing
---------------------------
Subclassing an enumeration is allowed only if the enumeration does not define
A new :class:`Enum` class must have one base Enum class, up to one concrete
data type, and as many :class:`object`-based mixin classes as needed. The
order of these base classes is::
def EnumName([mix-in, ...,] [data-type,] base-enum):
pass
Also, subclassing an enumeration is allowed only if the enumeration does not define
any members. So this is forbidden::
>>> class MoreColor(Color):

48
Lib/enum.py
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@ -480,37 +480,25 @@ class EnumMeta(type):
if not bases:
return object, Enum
# double check that we are not subclassing a class with existing
# enumeration members; while we're at it, see if any other data
# type has been mixed in so we can use the correct __new__
member_type = first_enum = None
for base in bases:
if (base is not Enum and
issubclass(base, Enum) and
base._member_names_):
raise TypeError("Cannot extend enumerations")
# base is now the last base in bases
if not issubclass(base, Enum):
raise TypeError("new enumerations must be created as "
"`ClassName([mixin_type,] enum_type)`")
def _find_data_type(bases):
for chain in bases:
for base in chain.__mro__:
if base is object:
continue
elif '__new__' in base.__dict__:
if issubclass(base, Enum) and not hasattr(base, '__new_member__'):
continue
return base
# get correct mix-in type (either mix-in type of Enum subclass, or
# first base if last base is Enum)
if not issubclass(bases[0], Enum):
member_type = bases[0] # first data type
first_enum = bases[-1] # enum type
else:
for base in bases[0].__mro__:
# most common: (IntEnum, int, Enum, object)
# possible: (<Enum 'AutoIntEnum'>, <Enum 'IntEnum'>,
# <class 'int'>, <Enum 'Enum'>,
# <class 'object'>)
if issubclass(base, Enum):
if first_enum is None:
first_enum = base
else:
if member_type is None:
member_type = base
# ensure final parent class is an Enum derivative, find any concrete
# data type, and check that Enum has no members
first_enum = bases[-1]
if not issubclass(first_enum, Enum):
raise TypeError("new enumerations should be created as "
"`EnumName([mixin_type, ...] [data_type,] enum_type)`")
member_type = _find_data_type(bases) or object
if first_enum._member_names_:
raise TypeError("Cannot extend enumerations")
return member_type, first_enum

199
Lib/test/test_enum.py
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@ -122,6 +122,22 @@ class TestHelpers(unittest.TestCase):
'__', '___', '____', '_____',):
self.assertFalse(enum._is_dunder(s))
# for subclassing tests
class classproperty:
def __init__(self, fget=None, fset=None, fdel=None, doc=None):
self.fget = fget
self.fset = fset
self.fdel = fdel
if doc is None and fget is not None:
doc = fget.__doc__
self.__doc__ = doc
def __get__(self, instance, ownerclass):
return self.fget(ownerclass)
# tests
class TestEnum(unittest.TestCase):
@ -1730,6 +1746,102 @@ class TestEnum(unittest.TestCase):
else:
raise Exception('Exception not raised.')
def test_multiple_mixin(self):
class MaxMixin:
@classproperty
def MAX(cls):
max = len(cls)
cls.MAX = max
return max
class StrMixin:
def __str__(self):
return self._name_.lower()
class SomeEnum(Enum):
def behavior(self):
return 'booyah'
class AnotherEnum(Enum):
def behavior(self):
return 'nuhuh!'
def social(self):
return "what's up?"
class Color(MaxMixin, Enum):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(Color.RED.value, 1)
self.assertEqual(Color.GREEN.value, 2)
self.assertEqual(Color.BLUE.value, 3)
self.assertEqual(Color.MAX, 3)
self.assertEqual(str(Color.BLUE), 'Color.BLUE')
class Color(MaxMixin, StrMixin, Enum):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(Color.RED.value, 1)
self.assertEqual(Color.GREEN.value, 2)
self.assertEqual(Color.BLUE.value, 3)
self.assertEqual(Color.MAX, 3)
self.assertEqual(str(Color.BLUE), 'blue')
class Color(StrMixin, MaxMixin, Enum):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(Color.RED.value, 1)
self.assertEqual(Color.GREEN.value, 2)
self.assertEqual(Color.BLUE.value, 3)
self.assertEqual(Color.MAX, 3)
self.assertEqual(str(Color.BLUE), 'blue')
class CoolColor(StrMixin, SomeEnum, Enum):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(CoolColor.RED.value, 1)
self.assertEqual(CoolColor.GREEN.value, 2)
self.assertEqual(CoolColor.BLUE.value, 3)
self.assertEqual(str(CoolColor.BLUE), 'blue')
self.assertEqual(CoolColor.RED.behavior(), 'booyah')
class CoolerColor(StrMixin, AnotherEnum, Enum):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(CoolerColor.RED.value, 1)
self.assertEqual(CoolerColor.GREEN.value, 2)
self.assertEqual(CoolerColor.BLUE.value, 3)
self.assertEqual(str(CoolerColor.BLUE), 'blue')
self.assertEqual(CoolerColor.RED.behavior(), 'nuhuh!')
self.assertEqual(CoolerColor.RED.social(), "what's up?")
class CoolestColor(StrMixin, SomeEnum, AnotherEnum):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(CoolestColor.RED.value, 1)
self.assertEqual(CoolestColor.GREEN.value, 2)
self.assertEqual(CoolestColor.BLUE.value, 3)
self.assertEqual(str(CoolestColor.BLUE), 'blue')
self.assertEqual(CoolestColor.RED.behavior(), 'booyah')
self.assertEqual(CoolestColor.RED.social(), "what's up?")
class ConfusedColor(StrMixin, AnotherEnum, SomeEnum):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(ConfusedColor.RED.value, 1)
self.assertEqual(ConfusedColor.GREEN.value, 2)
self.assertEqual(ConfusedColor.BLUE.value, 3)
self.assertEqual(str(ConfusedColor.BLUE), 'blue')
self.assertEqual(ConfusedColor.RED.behavior(), 'nuhuh!')
self.assertEqual(ConfusedColor.RED.social(), "what's up?")
class ReformedColor(StrMixin, IntEnum, SomeEnum, AnotherEnum):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(ReformedColor.RED.value, 1)
self.assertEqual(ReformedColor.GREEN.value, 2)
self.assertEqual(ReformedColor.BLUE.value, 3)
self.assertEqual(str(ReformedColor.BLUE), 'blue')
self.assertEqual(ReformedColor.RED.behavior(), 'booyah')
self.assertEqual(ConfusedColor.RED.social(), "what's up?")
self.assertTrue(issubclass(ReformedColor, int))
class TestOrder(unittest.TestCase):
@ -2093,6 +2205,49 @@ class TestFlag(unittest.TestCase):
d = 6
self.assertEqual(repr(Bizarre(7)), '<Bizarre.d|c|b: 7>')
def test_multiple_mixin(self):
class AllMixin:
@classproperty
def ALL(cls):
members = list(cls)
all_value = None
if members:
all_value = members[0]
for member in members[1:]:
all_value |= member
cls.ALL = all_value
return all_value
class StrMixin:
def __str__(self):
return self._name_.lower()
class Color(AllMixin, Flag):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(Color.RED.value, 1)
self.assertEqual(Color.GREEN.value, 2)
self.assertEqual(Color.BLUE.value, 4)
self.assertEqual(Color.ALL.value, 7)
self.assertEqual(str(Color.BLUE), 'Color.BLUE')
class Color(AllMixin, StrMixin, Flag):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(Color.RED.value, 1)
self.assertEqual(Color.GREEN.value, 2)
self.assertEqual(Color.BLUE.value, 4)
self.assertEqual(Color.ALL.value, 7)
self.assertEqual(str(Color.BLUE), 'blue')
class Color(StrMixin, AllMixin, Flag):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(Color.RED.value, 1)
self.assertEqual(Color.GREEN.value, 2)
self.assertEqual(Color.BLUE.value, 4)
self.assertEqual(Color.ALL.value, 7)
self.assertEqual(str(Color.BLUE), 'blue')
@support.reap_threads
def test_unique_composite(self):
# override __eq__ to be identity only
@ -2468,6 +2623,49 @@ class TestIntFlag(unittest.TestCase):
for f in Open:
self.assertEqual(bool(f.value), bool(f))
def test_multiple_mixin(self):
class AllMixin:
@classproperty
def ALL(cls):
members = list(cls)
all_value = None
if members:
all_value = members[0]
for member in members[1:]:
all_value |= member
cls.ALL = all_value
return all_value
class StrMixin:
def __str__(self):
return self._name_.lower()
class Color(AllMixin, IntFlag):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(Color.RED.value, 1)
self.assertEqual(Color.GREEN.value, 2)
self.assertEqual(Color.BLUE.value, 4)
self.assertEqual(Color.ALL.value, 7)
self.assertEqual(str(Color.BLUE), 'Color.BLUE')
class Color(AllMixin, StrMixin, IntFlag):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(Color.RED.value, 1)
self.assertEqual(Color.GREEN.value, 2)
self.assertEqual(Color.BLUE.value, 4)
self.assertEqual(Color.ALL.value, 7)
self.assertEqual(str(Color.BLUE), 'blue')
class Color(StrMixin, AllMixin, IntFlag):
RED = auto()
GREEN = auto()
BLUE = auto()
self.assertEqual(Color.RED.value, 1)
self.assertEqual(Color.GREEN.value, 2)
self.assertEqual(Color.BLUE.value, 4)
self.assertEqual(Color.ALL.value, 7)
self.assertEqual(str(Color.BLUE), 'blue')
@support.reap_threads
def test_unique_composite(self):
# override __eq__ to be identity only
@ -2553,6 +2751,7 @@ class TestUnique(unittest.TestCase):
value = 4
expected_help_output_with_docs = """\
Help on class Color in module %s:

1
Misc/NEWS.d/next/Library/2018-09-14-20-00-47.bpo-29577.RzwKFD.rst Normal file
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@ -0,0 +1 @@
Support multiple mixin classes when creating Enums.