Iterate enum in definition order in Python 2

Question

I'm using the backported Enum functionality from python 3.4 with python 2.7:

> python --version
Python 2.7.6
> pip install enum34
# Installs version 1.0...

According to the documentation for Enums in python 3 (https://docs.python.org/3/library/enum.html#creating-an-enum), "Enumerations support iteration, in definition order". However, iteration is not happening in order for me:

>>> from enum import Enum
>>> class Shake(Enum):
...     vanilla = 7
...     chocolate = 4
...     cookies = 9
...     mint = 3
...     
>>> for s in Shake:
...     print(s)
...     
Shake.mint
Shake.chocolate
Shake.vanilla
Shake.cookies

Am I misunderstanding something, or is iteration in definition order just not supported in the backported versions of Enums yet? Assuming the latter, is there an easy way to force it to happen in order?

Answer 1

I found the answer here: https://pypi.python.org/pypi/enum34/1.0.

For python <3.0, you need to specify an __order__ attribute:

>>> from enum import Enum
>>> class Shake(Enum):
...     __order__ = 'vanilla chocolate cookies mint'
...     vanilla = 7
...     chocolate = 4
...     cookies = 9
...     mint = 3
...     
>>> for s in Shake:
...     print(s)
...     
Shake.vanilla
Shake.chocolate
Shake.cookies
Shake.mint

Answer 2

use

__order__ 

to define the order of enums for python version less than 3 . It is not necessary in python3 but make sure the order which is supplied same as declared order otherwise it will give error:

TypeError: member order does not match _order_


import enum


class EXCHANGE(enum.Enum):
    __order__ = " EXCHANGE_NSE EXCHANGE_BSE EXCHANGE_NFO EXCHANGE_CDS EXCHANGE_BFO EXCHANGE_MCX EXCHANGE_BCD "
    EXCHANGE_NSE = "NSE"
    EXCHANGE_BSE = "BSE"
    EXCHANGE_NFO = "NFO"
    EXCHANGE_CDS = "CDS"
    EXCHANGE_BFO = "BFO"
    EXCHANGE_MCX = "MCX"
    EXCHANGE_BCD = "BCD"


if __name__ == "__main__":
    for ex in EXCHANGE:
        print(f"{ex.name} : {ex.value}")

Output:

EXCHANGE_NSE : NSE
EXCHANGE_BSE : BSE
EXCHANGE_NFO : NFO
EXCHANGE_CDS : CDS
EXCHANGE_BFO : BFO
EXCHANGE_MCX : MCX
EXCHANGE_BCD : BCD