Python Enum class (with tostring fromstring)

Question

I've found a simply way to implement(hack) an enum into Python:

class MyEnum:
  VAL1, VAL2, VAL3 = range(3)

I can then call this as such:

bob = MyEnum.VAL1

Sexy!

Alright, now I want to be able to get both the numerical value if given a string, or a string if given a numerical value. Let's say I want the strings to exactly match up to the Enum key's

The best I could think of is something like this:

class MyEnum:
  VAL1, VAL2, VAL3 = range(3)
  @classmethod
  def tostring(cls, val):
    if (val == cls.VAL1):
      return "VAL1"
    elif (val == cls.VAL2):
      return "VAL2"
    elif (val == cls.VAL3):
      return "VAL3"
    else:
      return None
  @classmethod
  def fromstring(cls, str):
    if (str.upper() == "VAL1"):
      return cls.VAL1
    elif (str.upper() == "VAL2"):
      return cls.VAL2
    elif (str.upper() == "VAL2"):
      return cls.VAL2
    else:
      return None

or something like that (ignore how i'm catching invalid cases)

Is there a better, more python centric way to do what I'm doing above? Or is the above already as concise as it gets.

It seems like there's got to be a better way to do it.

Answer 1

Well, here is what you asked for:

class MyEnum:
  VAL1, VAL2, VAL3 = range(3)
  @classmethod
  def tostring(cls, val):
    for k,v in vars(cls).iteritems():
        if v==val:
            return k

  @classmethod
  def fromstring(cls, str):
      return getattr(cls, str.upper(), None)

print MyEnum.fromstring('Val1')
print MyEnum.tostring(2)

But I really don't get the point of Enums in Python. It has such a rich type system as well as generators and coroutines to manage states.

I know I've not been using Enums in Python for more than 12 years, maybe you can get rid of them too ;-)