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December 3, 2023 20:31
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Dynamic Python Enums; Create an `enum.Enum` with members defined in a `dict`
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| """I saw on StackOverflow _It isn't possible_ - then I asked GPT, and it parroted the stack overflow answer. | |
| In this example we wish to create a ready-to-use Enum extended class. | |
| class Cooked(Enum): | |
| POP = 'pop' | |
| FOO = 'foo' | |
| This, with the ability to append new enums members. | |
| Understandably this cannot be done _after_ the Enum is defined, | |
| as they special c things (not a generic object type) - so they act a bit strange under the `type()`. | |
| But we can build the `Cooked` class dynamically using the same typing: | |
| members = { | |
| 'POP': 'pop', | |
| 'FOO': 'foo', | |
| 'EGG': 'egg' | |
| } | |
| Cooked = generate_enum('Cooked', members) | |
| Under-the-hood this essentially _writes_ the class definition as if we wrote it manually, this is hoisted as a normal class. | |
| --- | |
| Notably there is a library called `aenum` that performs the same. So rock-on aenum (\m/ >.< \m/); it clearly is possible. | |
| """ | |
| from enum import Enum, EnumMeta | |
| import enum | |
| class DynamicStrEnum(EnumMeta): | |
| def __new__(metacls, cls, bases=None, classdict=None): | |
| init_members = classdict or {} | |
| enum_dict = enum._EnumDict() | |
| bases = bases or (Enum,) | |
| for key, value in init_members.items(): | |
| enum_dict[key] = value | |
| props = type(enum_dict)() | |
| props['has'] = classmethod(has) | |
| for key in enum_dict._member_names: | |
| value = enum_dict[key] | |
| props[key] = key.lower() if len(value) == 0 else value | |
| names = set(enum_dict._member_names) | |
| for key, value in enum_dict.items(): | |
| if key in names: | |
| continue | |
| props[key] = value | |
| return super(DynamicStrEnum, metacls).__new__(metacls, | |
| cls, bases, props) | |
| class CookedBase(Enum): | |
| """The base for the dynamic bake content | |
| """ | |
| alt_has = classmethod(has) | |
| def generate_enum(name, members_dict, enum_bases=None): | |
| """Build and return a new Enum class | |
| Baked = DynamicStrEnum('Cooked', (CookedBase,), get_members()) | |
| """ | |
| return DynamicStrEnum(name, enum_bases or (CookedBase,), members_dict) | |
| def has(cls, value): | |
| return value in cls._value2member_map_ | |
| class Cooked(Enum): | |
| """An existing (already cooked) enum | |
| """ | |
| POP = 'pop' | |
| FOO = 'foo' | |
| @classmethod | |
| def has(cls, value): | |
| return value in cls._value2member_map_ | |
| members = { | |
| 'POP': 'pop', | |
| 'FOO': 'foo', | |
| 'EGG': 'egg' | |
| } | |
| Baked = generate_enum('Cooked', members) | |
| # Usage | |
| assert Baked.POP.value == Cooked.POP.value | |
| assert Baked.has('pop') | |
| assert Baked.alt_has == Baked.has | |
| assert Cooked.has('pop') |
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