ref: 4410517b44fd2610abe0dcd1349bb3e6b3c5ddb8
dir: /sys/src/cmd/python/Demo/newmetaclasses/Enum.py/
"""Enumeration metaclass.""" class EnumMetaclass(type): """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__(cls, name, bases, dict): super(EnumMetaclass, cls).__init__(name, bases, dict) cls._members = [] for attr in dict.keys(): if not (attr.startswith('__') and attr.endswith('__')): enumval = EnumInstance(name, attr, dict[attr]) setattr(cls, attr, enumval) cls._members.append(attr) def __getattr__(cls, name): if name == "__members__": return cls._members raise AttributeError, name def __repr__(cls): s1 = s2 = "" enumbases = [base.__name__ for base in cls.__bases__ if isinstance(base, EnumMetaclass) and not base is Enum] if enumbases: s1 = "(%s)" % ", ".join(enumbases) enumvalues = ["%s: %d" % (val, getattr(cls, val)) for val in cls._members] if enumvalues: s2 = ": {%s}" % ", ".join(enumvalues) return "%s%s%s" % (cls.__name__, s1, s2) class FullEnumMetaclass(EnumMetaclass): """Metaclass for full enumerations. A full enumeration displays all the values defined in base classes. """ def __init__(cls, name, bases, dict): super(FullEnumMetaclass, cls).__init__(name, bases, dict) for obj in cls.__mro__: if isinstance(obj, EnumMetaclass): for attr in obj._members: # XXX inefficient if not attr in cls._members: cls._members.append(attr) class EnumInstance(int): """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 __new__(cls, classname, enumname, value): return int.__new__(cls, value) def __init__(self, classname, enumname, value): self.__classname = classname self.__enumname = enumname def __repr__(self): return "EnumInstance(%s, %s, %d)" % (self.__classname, self.__enumname, self) def __str__(self): return "%s.%s" % (self.__classname, self.__enumname) class Enum: __metaclass__ = EnumMetaclass class FullEnum: __metaclass__ = FullEnumMetaclass def _test(): class Color(Enum): red = 1 green = 2 blue = 3 print Color.red print repr(Color.red) 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 def _test2(): class Color(FullEnum): red = 1 green = 2 blue = 3 print Color.red print repr(Color.red) 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(FullEnum): 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() _test2()