Is there a better way to get a named series of constants (enumeration) in Python? [duplicate]

Answer 1

The following acts like a classisc "written in stone" C enum -- once defined, you can't change it, you can only read its values. Neither can you instantiate it. All you have to do is "import enum.py" and derive from class Enum.

# this is enum.py
class EnumException( Exception ):
   pass

class Enum( object ):
   class __metaclass__( type ):
      def __setattr__( cls, name, value ):
         raise EnumException("Can't set Enum class attribute!")
      def __delattr__( cls, name ):
         raise EnumException("Can't delete Enum class attribute!")

   def __init__( self ):
      raise EnumException("Enum cannot be instantiated!")

This is the test code:

# this is testenum.py
from enum import *

class ExampleEnum( Enum ):
   A=1
   B=22
   C=333

if __name__ == '__main__' :

   print "ExampleEnum.A |%s|" % ExampleEnum.A
   print "ExampleEnum.B |%s|" % ExampleEnum.B
   print "ExampleEnum.C |%s|" % ExampleEnum.C
   z = ExampleEnum.A
   if z == ExampleEnum.A:
      print "z is A"

   try:
       ExampleEnum.A = 4   
       print "ExampleEnum.A |%s| FAIL!" % ExampleEnum.A
   except EnumException:
       print "Can't change Enum.A (pass...)"

   try:
       del ExampleEnum.A
   except EnumException:
       print "Can't delete Enum.A (pass...)"

   try:
       bad = ExampleEnum()
   except EnumException:
       print "Can't instantiate Enum (pass...)"