ref: 34f5a8333090c5090e1d0b6ddbaf900d64340eea
dir: /sys/src/cmd/python/Demo/metaclasses/Enum.py/
"""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()