[Python-Dev] PEP 435 - reference implementation discussion (original) (raw)

Tim Delaney timothy.c.delaney at gmail.com
Sun May 5 05:50:25 CEST 2013

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Split off from the PEP 435 - requesting pronouncement thread.

Think I've come up with a system that works for my auto-numbering case without knowing the internals of enum_type. Patch passes all existing test cases. The patch does two things:

1. Finds the first non-Enum class on the MRO of the new class and uses that as the enum type.

2. Instead of directly setting the _name and _value of the enum_item, it lets the Enum class do it via Enum.init(). Subclasses can override this. This gives Enums a 2-phase construction just like other classes.

diff -r 758d43b9f732 ref435.py --- a/ref435.py Fri May 03 18:59:32 2013 -0700 +++ b/ref435.py Sun May 05 13:43:56 2013 +1000 @@ -116,7 +116,17 @@ if bases[-1] is Enum: obj_type = bases[0] else:

•            obj_type = bases[-1].__mro__[1] # e.g. (IntEnum, int,

Enum, object)

•            obj_type = None

•            for base in bases:

•                for c in base.__mro__:

•                    if not issubclass(c, Enum):

•                        obj_type = c

•                        break

•                if obj_type is not None:

•                    break

•     else:
          obj_type = object
      # save enum items into separate mapping so they don't get baked

into @@ -143,8 +153,7 @@ enum_item = object.new(enum_class) else: enum_item = obj_type.new(enum_class, value)

•            enum_item._value = value

•            enum_item._name = e

•            enum_item.__init__(e, value)
         enum_map[e] = enum_item
     enum_class.__aliases__ = aliases      # non-unique enums names
     enum_class._enum_names = enum_names     # enum names in definition

order @@ -232,6 +241,10 @@ return enum raise ValueError("%s is not a valid %s" % (value, cls.name))

• def init(self, name, value):

•    self._name = name

•    self._value = value

• def __repr__(self):
      return "<%s.%s: %r>" % (self.__class__.__name__, self._name,

self._value)

Auto-int implementation:

class AutoInt(int): slots = ()

def __new__(cls, value):
    if value is Ellipsis:
        try:
            i = cls._auto_number
        except AttributeError:
            i = cls._auto_number = 0

    else:
        i = cls._auto_number = value

    cls._auto_number += 1
    return int.__new__(cls, i)

class AutoIntEnum(AutoInt, IntEnum): def init(self, name, value): super(AutoIntEnum, self).init(name, int(self))

class TestAutoIntEnum(AutoIntEnum): a = ... b = 3 c = ...

class TestAutoIntEnum2(AutoIntEnum): a = ... b = ... c = ...

print(TestAutoIntEnum, list(TestAutoIntEnum)) print(TestAutoIntEnum2, list(TestAutoIntEnum2))

---------- Run ---------- <Enum 'TestAutoIntEnum'> [<TestAutoIntEnum.a: 0>, <TestAutoIntEnum.b: 3>, <TestAutoIntEnum.c: 4>] <Enum 'TestAutoIntEnum2'> [<TestAutoIntEnum2.a: 0>, <TestAutoIntEnum2.b: 1>, <TestAutoIntEnum2.c: 2>]

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