Python 3 Enums with Function Values

Question

I noticed an oddity in the Python 3 Enums (link).
If you set the value of an Enum to a function, it prevents the attribute from being wrapped as an Enum object, which prevents you from being able to use the cool features like EnumCls['AttrName'] to dynamically load the attribute.

Is this a bug? Done on purpose?
I searched for a while but found no mention of restricted values that you can use in an Enum.

Here is sample code that displays the issue:

class Color(Enum):
    Red = lambda: print('In Red')
    Blue = lambda: print('In Blue')

print(Color.Red)    # <function> - should be Color.Red via Docs
print(Color.Blue)   # <function> - should be Color.Bluevia Docs
print(Color['Red']) # throws KeyError - should be Color.Red via Docs

Also, this is my first time asking, so let me know if there's anything I should be doing differently! And thanks for the help!

Answer 1

You can override the __call__ method:

from enum import Enum, auto

class Color(Enum):
    red = auto()
    blue = auto()

    def __call__(self, *args, **kwargs):
        return f'<font color={self.name}>{args[0]}</font>'

Can then be used:

>>> Color.red('flowers')
<font color=red>flowers</font>

Answer 2

The documentation says:

The rules for what is allowed are as follows: _sunder_ names (starting and ending with a single underscore) are reserved by enum and cannot be used; all other attributes defined within an enumeration will become members of this enumeration, with the exception of __dunder__ names and descriptors (methods are also descriptors).

A "method" is just a function defined inside a class body. It doesn't matter whether you define it with lambda or def. So your example is the same as:

class Color(Enum):
    def Red():
        print('In Red')
    def Blue():
        print('In Blue')

In other words, your purported enum values are actually methods, and so won't become members of the Enum.

Answer 3

If someone need/want to use Enum with functions as values, its possible to do so by using a callable object as a proxy, something like this:

class FunctionProxy:
    """Allow to mask a function as an Object."""
    def __init__(self, function):
        self.function = function

    def __call__(self, *args, **kwargs):
        return self.function(*args, **kwargs)

A simple test:

from enum import Enum
class Functions(Enum):
    Print_Function = FunctionProxy(lambda *a: print(*a))
    Split_Function = FunctionProxy(lambda s, d='.': s.split(d))

Functions.Print_Function.value('Hello World!')
# Hello World!
Functions.Split_Function.value('Hello.World.!')
# ['Hello', 'World', '!']