ref: 5ebb1a29d8250027e8b7f2287f3bfa3a6f3d13ac
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()