Adding members to Python Enums

Question

I understand that this is NOT the standard use case, but I need to dynamically add elements to a IntEnum derived class in Python. Notice that dynamically creating the Enum using the functional API is not enough. I need to add elements to an existing enum. How can I do this?

Background: For those of you wondering why would somebody want to do this. I am wrapping a library and the values for the enum are defined within the library. I can query the names and values using the library API. But I cannot do it upon initialization as it depends on components which are dynamically loaded by the library upon user request. I could load all components at start up and use the functional API to create the enum upon import but this is time consuming and has side effects.

Answer 1

This is a job for the extend_enum function from the aenum library¹.

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A couple sample Enums:

from aenum import Enum

class Color(Enum):
    black = 0

class ColorHelp(Enum):
    _init_ = 'value __doc__'
    black = 0, 'the absence of color'

extend_enum in action:

from aenum import extend_enum

extend_enum(Color, 'white', 1)
print Color, list(Color)
print repr(Color.black), Color.black, repr(Color.white), Color.white
print

extend_enum(ColorHelp, 'white', 1, 'the presence of every color')
print ColorHelp, list(ColorHelp)
print repr(ColorHelp.black), ColorHelp.black, ColorHelp.black.__doc__, repr(ColorHelp.white), ColorHelp.white, ColorHelp.white.__doc__

Which gives us:

<enum 'Color'> [<Color.black: 0>, <Color.white: 1>]
<Color.black: 0> Color.black <Color.white: 1> Color.white

<enum 'ColorHelp'> [<ColorHelp.black: 0>, <ColorHelp.white: 1>]
<ColorHelp.black: 0> ColorHelp.black the absence of color <ColorHelp.white: (1, 'the presence of every color')> ColorHelp.white None

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¹ Disclosure: I am the author of the Python stdlib Enum, the enum34 backport, and the Advanced Enumeration (aenum) library.