"""Enumeration metaclass.

XXX This is very much a work in progress.

"""

import string

class EnumMetaClass:

    """Metaclass for enumeration.

    To define your own enumeration, do something like

    class Color(Enum):

        red = 1

        green = 2

        blue = 3

    Now, Color.red, Color.green and Color.blue behave totally

    different: they are enumerated values, not integers.

    Enumerations cannot be instantiated; however they can be

    subclassed.

    """

    def __init__(self, name, bases, dict):

        """Constructor -- create an enumeration.

        Called at the end of the class statement.  The arguments are

        the name of the new class, a tuple containing the base

        classes, and a dictionary containing everything that was

        entered in the class' namespace during execution of the class

        statement.  In the above example, it would be {'red': 1,

        'green': 2, 'blue': 3}.

        """

        for base in bases:

            if base.__class__ is not EnumMetaClass:

                raise TypeError, "Enumeration base class must be enumeration"

        bases = filter(lambda x: x is not Enum, bases)

        self.__name__ = name

        self.__bases__ = bases

        self.__dict = {}

        for key, value in dict.items():

            self.__dict[key] = EnumInstance(name, key, value)

    def __getattr__(self, name):

        """Return an enumeration value.

        For example, Color.red returns the value corresponding to red.

        XXX Perhaps the values should be created in the constructor?

        This looks in the class dictionary and if it is not found

        there asks the base classes.

        The special attribute __members__ returns the list of names

        defined in this class (it does not merge in the names defined

        in base classes).

        """

        if name == '__members__':

            return self.__dict.keys()

        try:

            return self.__dict[name]

        except KeyError:

            for base in self.__bases__:

                try:

                    return getattr(base, name)

                except AttributeError:

                    continue

        raise AttributeError, name

    def __repr__(self):

        s = self.__name__

        if self.__bases__:

            s = s + '(' + string.join(map(lambda x: x.__name__,

                                          self.__bases__), ", ") + ')'

        if self.__dict:

            list = []

            for key, value in self.__dict.items():

                list.append("%s: %s" % (key, int(value)))

            s = "%s: {%s}" % (s, string.join(list, ", "))

        return s

class EnumInstance:

    """Class to represent an enumeration value.

    EnumInstance('Color', 'red', 12) prints as 'Color.red' and behaves

    like the integer 12 when compared, but doesn't support arithmetic.

    XXX Should it record the actual enumeration rather than just its

    name?

    """

    def __init__(self, classname, enumname, value):

        self.__classname = classname

        self.__enumname = enumname

        self.__value = value

    def __int__(self):

        return self.__value

    def __repr__(self):

        return "EnumInstance(%r, %r, %r)" % (self.__classname,

                                             self.__enumname,

                                             self.__value)

    def __str__(self):

        return "%s.%s" % (self.__classname, self.__enumname)

    def __cmp__(self, other):

        return cmp(self.__value, int(other))

# Create the base class for enumerations.

# It is an empty enumeration.

Enum = EnumMetaClass("Enum", (), {})

def _test():

    class Color(Enum):

        red = 1

        green = 2

        blue = 3

    print Color.red

    print dir(Color)

    print Color.red == Color.red

    print Color.red == Color.blue

    print Color.red == 1

    print Color.red == 2

    class ExtendedColor(Color):

        white = 0

        orange = 4

        yellow = 5

        purple = 6

        black = 7

    print ExtendedColor.orange

    print ExtendedColor.red

    print Color.red == ExtendedColor.red

    class OtherColor(Enum):

        white = 4

        blue = 5

    class MergedColor(Color, OtherColor):

        pass

    print MergedColor.red

    print MergedColor.white

    print Color

    print ExtendedColor

    print OtherColor

    print MergedColor

if __name__ == '__main__':

    _test()