cutecat@amiau:~/cpython$ cat /tmp/innerplanets.py 
from enum import Enum

class innerplanets(Enum):
    mercury = 1
    venus = 2
    earth = 3
    mars = 4

for planet in innerplanets:
    print(planet)
for planet in reversed(innerplanets):
    print(planet)
cutecat@amiau:~/cpython$ ./python /tmp/innerplanets.py 
innerplanets.mercury
innerplanets.venus
innerplanets.earth
innerplanets.mars
Traceback (most recent call last):
  File "/tmp/innerplanets.py", line 11, in <module>
    for planet in reversed(innerplanets):
  File "/home/cutecat/cpython/Lib/enum.py", line 255, in __getitem__
    return cls._member_map_[name]
KeyError: 3

Attached the patch to add support for reversed in enum.