Python enums with complex types

Question

I'm new to Python and I'm wondering if I can build enums with complex structures, not just primitive types. For instance (in pseudo-code):

Point::Enum
  x, y
  constructor ( x, y ) {
    ...
  }

  bottom_left = Point ( 0, 0 )
  top_left = Point ( 0, 100 )
  top_right = Point ( 100, 100 )
  bottom_right = Point ( 100, 0 )

So far, I could only find Python documentation that mentions enums with strings or ints.

There is no restriction on type, plus in Python strings and ints are 'complex types'. — pvg, Jun 07 '16 at 11:48
OK, there aren't, yet 1 or 'blah' are rather different than (0,0) :-) — zakmck, Jun 07 '16 at 12:30

Ethan Furman · Accepted Answer · 2018-08-15T18:41:28.950

If you want Point as a separate entity from the Enum that tracks the corners, then you need them to be separate:

from enum import Enum

class Point(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __repr__(self):
        return 'Point(%r, %r)' % (self.x, self.y)

class Corner(Enum):
    BottomLeft = Point(0, 0)
    TopLeft = Point(0, 100)
    TopRight = Point(100, 100)
    BottmRight = Point(100, 0)

Doing it this way means that each enum contains a Point as its value, but is not a Point itself:

>>> Corner.BottomLeft
<Corner.BottomLeft: Point(0, 0)>
>>> Corner.BottomLeft.value
Point(0, 0)

If you want the enum members to be a Point, then mix in the Point class:

from enum import Enum

class Point(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def __repr__(self):
        return 'Point(%r, %r)' % (self.x, self.y)

class Corner(Point, Enum):
    BottomLeft = 0, 0
    TopLeft = 0, 100
    TopRight = 100, 100
    BottmRight = 100, 0

>>> Corner.TopLeft
<Corner.TopLeft: (0, 0)>
>>> isinstance(Corner.TopLeft, Point)
True
>>> Corner.TopLeft.value
(0, 100)
>>> Corner.TopLeft.x
0
>>> Corner.TopLeft.y
100

Finally, if all you need is for the enums to have the x and y attributes:

from aenum import Enum

class Corner(Enum):
    __init__ = 'x y'
    BottomLeft = 0, 0
    TopLeft = 0, 100
    TopRight = 100, 100
    BottmRight = 100, 0

>>> Corner.TopLeft
<Corner.TopLeft: (0, 100)>
>>> Corner.TopLeft.value
(0, 100)
>>> Corner.TopLeft.x
0
>>> Corner.TopLeft.y
100

Note that that last example is using the aenum package¹. You can accomplish the same thing with either enum34 or the stdlib enum by writing an __init__ for the Point class.

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

score 0 · Answer 2 · answered Jun 07 '16 at 11:52

Try this:

class Point(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y

class Enum:
    bottom_left = Point(0, 0)
    top_left = Point(0, 100)
    top_right = Point(100, 100)
    bottom_right = Point(100, 0)

score 0 · Answer 3 · answered Jun 07 '16 at 12:02

You can declare them as global variables like BOTTOM_LEFT, TOP_LEFT, TOP_RIGHT, BOTTOM_RIGHT.

As you might be aware unlike other languages (C++, Java) Python doesn't have, You just declare it and don't change it (Gentleman's game)

Yet Alex Martelli's recipe can come handy to emulate const in Python

Python enums with complex types

3 Answers3