On 04/16/2017 01:24 AM, Steven D'Aprano wrote:
On Fri, Apr 14, 2017 at 06:06:29PM -0700, Stephan Hoyer wrote:
One way that I've found myself using enums recently is for dispatching (as
keys in a dictionary) between different interchangeable functions or
classes.
[...]
Given that wanting to use a function as the enumeration value is quite
unusual in the first place, I don't think this belongs in the standard
library.
I agree with D'Aprano: such unusual usage does not belong in the stdlib.
Fortunately, there is the Advanced Enumeration (aenum) library*:
--- 8< -----------------------------------------------------------------
from aenum import Enum, enum
class CallableEnum(Enum):
def __new__(cls, *args, **kwds):
member = object.__new__(cls)
member._impl = args[0]
if member._impl.__doc__ is not None:
member._value_ = member._impl.__doc__
else:
member._value_ = repr(member._impl)
return member
def __call__(self, *args, **kwds):
return self._impl(*args, **kwds)
--- 8< -----------------------------------------------------------------
and in use
--- 8< -----------------------------------------------------------------
class TestEnum(CallableEnum):
@enum
def hello(text):
"a pleasant greeting"
print('hello,', text)
@enum
def goodbye(text):
print('goodbye,', text)
list(TestEnum)
# [
# <TestEnum.hello: 'a pleasant greeting'>,
# <TestEnum.goodbye: '<function goodbye at 0xb7264844>'>,
# ]
print(TestEnum.hello)
# TestEnum.hello
TestEnum.hello('how are you?')
# 'hello, how are you?'
TestEnum.goodbye('see you soon!')
# 'goodbye, see you soon!'
--- 8< -----------------------------------------------------------------
Note that it is possible to do the same thing using the stdlib Enum if
you create your own decorator (it must return a class instance) and a
slight rewrite of __new__ -- but I'll leave that as an exercise for the
reader.
--
~Ethan~
* Disclosure: I am the primary author of the stdlib Enum; I am also the
author if the enum34 backport and the aenum library.
enum34: https://pypi.python.org/pypi/enum34
aenum: https://pypi.python.org/pypi/aenum
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