dns_constants.py

class ValueConstant(object):
    _container = None
    _name = None

    def __init__(self, value):
        self.value = value


    def _realize(self, container, name):
        self._container = container
        self._name = name


    def __repr__(self):
        return "<%s.%s(%s)>" % (self._container.__name__, self._name, self.value)



class ConstantsContainer(object):
    def __init__(self, original):
        self.constants = []
        self.constantsMap = {}
        for k, v in original.__dict__.items():
            if isinstance(v, ValueConstant):
                v._realize(original, k)
                self.constants.append(v)
                self.constantsMap[k] = v

        self.original = original


    def __getattr__(self, name):
        return getattr(self.original, name)


    def lookupByName(self, name):
        return self.constantsMap[name]


    def lookupByValue(self, value):
        for c in self.constants:
            if c.value == value:
                return c



def constants(cls):
    return ConstantsContainer(cls)



@constants
class RECORDS(object):
    A = ValueConstant(1)
    NS = ValueConstant(2)
    AAAA = ValueConstant(28)

    @classmethod
    def isHost(cls, constant):
        return constant in (cls.A, cls.AAAA)


print RECORDS.A
print RECORDS.AAAA
print RECORDS.constants
print RECORDS.lookupByName("AAAA")
print RECORDS.lookupByValue(28)
print RECORDS.isHost(RECORDS.A)
print RECORDS.isHost(RECORDS.NS)