ref: bfbe4803191725a24151ae04068a18cada3824e4
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()